[lirilllllrllliliri 


GENERAL 


BY 


CHARLES    H.    LAKE,   M.A. 

: 

PRINCIPAL    OF    EAST    TKCHMCAL    HKill    SCHOOL 
CLEVELAND,    OHIO 


SILVER,   BURDETT   AND    COMPANY 

BOSTON  NEW  YORK  CHICAGO 


COPYRIGHT,  1917, 

BY  SILVER,  BURDETT  AND  COMPANY 
EDUCATION 


PREFACE 

THE  question  of  what  science  shall  be  taught  in  the 
first  year  of  the  regular  high  school,  or  in  the  eighth  or 
ninth  years  of  the  Junior  High  School,  is  becoming  one 
of  steadily  increasing  importance.  The  logical  course  for 
this  period  of  the  child's  school  life  seems  to  be  a  general 
course  in  those  elements  of  science  which  will  form  a 
foundation  for  the  sciences  which  usually  come  later  in  the 
high  school  courses  of  study,  and  which  will  give  the  best 
training  to  those  who  may  withdraw  from  school  at  the  end 
of  the  ninth  year.  For  a  number  of  years  physical  geog- 
raphy was  the  science  commonly  taught  in  the  ninth 
year.  Teachers  of  this  subject  found  that  in  order  to  do 
their  best  work,  it  was  necessary  to  give  a  considerable 
portion  of  their  time  to  teaching  the  elements  of  related 
sciences  such  as  physics,  chemistry,  and  botany.  The 
same  thing  was  true  of  the  teachers  of  the  biological 
sciences.  This  fact  furnishes  an  excellent  argument  for  the 
substitution  of  a  course  in  general  science  for  the  sciences 
which  were  formerly  taught  in  the  first  year  of  our  high 
schools. 

First  year  science  is  intended  for  immature  minds.  It 
must  be  presented  and  illustrated  in  such  a  way  that  the 
pupil  will  not  be  confused  with  terms  which  are  too  techni- 
cal nor  with  treatments  of  topics  which  are  too  advanced 
for  him.  The  course  should  be  so  organized  that  the 
pupil,  while  dealing  with  some  known  facts,  will  be  con- 


•:•..:,£     /  PREFACE 

tinuously  relating  them  to  phenomena  about  him  which 
are  of  vital  interest  to  him  and  also  will  be  gaining  the 
correct  ideas  of  science  study.  He  will  be  studying  those 
phenomena  which  relate  his  daily  existence  to  the  funda- 
mental principles  of  science. 

As  science  the  treatments  in  this  book  are  not  intended 
to  be  exhaustive.  They  are  however  intended  to  be  sci- 
entifically correct  as  far  as  they  go  and  there  are  no  facts 
which  will  need  to  be  unlearned  as  the  pupil  progresses 
in  his  scientific  study.  The  subjects  treated  are  those 
which  are  vitally  connected  with  our  daily  life  and  which 
are  also  worthy  of  study  as  organized  scientific  material. 
The  questions  asked  are  not  intended  to  be  exhaustive. 
They  are  merely  suggestive  and  should  be  supplemented 
with  many  others  by  the  teacher. 

The  object  in  such  a  course  of  study  as  in  all  other 
courses  of  study  should  be  to  teach  the  pupil  to  live,  regard- 
less of  whether  he  withdraws  from  school  at  an  early  date 
or  whether  he  continues  his  education  through  the  high 
school  and  college.  We  should  always  be  teaching  a 
pupil  "what  he  needs  and  what  he  can  use"  and  a  general 
science  course  well  taught  fulfils  this  ideal  admirably. 

There  should  not  be  a  great  deal  of  laboratory  work 
done  by  beginning  students  in  science.  Some  of  the  sug- 
gested experiments  in  the  text  should  be  performed  by 
the  teacher  while  others  are  quite  simple  and  may  well  be 
performed  by  the  pupils  at  home.  By  so  doing  they  will 
develop  self-reliance  and  the  varied  experiences  of  the 
members  of  the  class  will  bring  out  many  practical  relation- 
ships between  the  experiments  and  the  life  around  them. 
Experiments  are  not  ends  in  themselves  and  no  experi- 
ments should  be  performed  unless  some  emphasis  is 
placed  on  the  use  of  the  principles  involved. 


PREFACE  vii 

The  author  desires  to  make  grateful  acknowledgment 
to  the  following  individuals,  manufacturers,  and  depart- 
ments of  the  United  States  Government,  who  have  so 
materially  assisted  in  collecting  the  illustrative  material : 
Professor  McAdie,  Blue  Hill  Observatory,  Readville, 
Mass. ;  H.  A.  Hutchins ;  Dr.  J.  A.  Bownocker ;  The 
Philadelphia  Museums ;  The  Warner  and  Swasey  Com- 
pany ;  Prest-o-Lite  Company ;  Cutler  Hammer  Manu- 
facturing Company;  Niagara  Falls  Power  Company; 
H.  Koppers  Company ;  Landers-Frary  Company ;  Davey 
Tree  Expert  Company;  Chicago,  Milwaukee  and  St.  Paul 
Rail  Road ;  A.  I.  Root  Company ;  Wright-Martin  Com- 
pany ;  Swift  and  Company ;  U.  S.  Navy  Department ; 
Bureau  of  Standards,  Washington,  D.  C. ;  U.  S.  Geologi- 
cal Survey;  U.  S.  Weather  Bureau;  U.  S.  Department 
of  Agriculture ;  U.  S.  Reclamation  Service ;  Forest  Serv- 
ice, Washington,  D.  C. ;  Ohio  Agricultural  Experiment 
Station. 

C.  H.  L. 


CONTENTS 

CHAPTER   I 

PAGE 

THE  EARTH          ....         ...         .         .         .         .         1 

The  Earth  and  its  Relation  to  the  Universe.  —  The 
Planets.  —  Satellites  or  Moons.  —  Planetoids  and  Comets. 
-  Stars.  —  Constellations.  —  The  North  Star.  —  The 
Moon.  —  Phases  of  the  Moon.  —  The  Sun.  —  Shape  of  the 
Earth.  —  Cause  of  the  Shape  of  the  Earth.  —  Size  of  the 
Earth.  —  Consequences  of  the  Shape  and  Size  of  the  Earth. 
—  Structure  of  the  Earth.  —  Motions  of  the  Earth.  — 
Rotation.  —  Directions.  —  The  Celestial  Meridian.  — 
Meridians  and  Parallels.  —  Latitude  and  Longitude.  — 
Local  Time.  —  Standard  Time.  —  Revolution  of  the  Earth. 
—  Change  of  Seasons. 


CHAPTER   II 

MATTER  AND  ITS  PROPERTIES    .         .       V        ....       26 

Constitution  of  Matter.  —  Properties  of  Matter.  —  Meas- 
urement. —  The  Metric  System.  —  Metric  Tables.  —  The 
Measurement  of  Length.  —  The  Measurement  of  Volume.  — 
The  Measurement  of  Mass.  —  Density  and  Specific  Gravity. 
—  Densities  of  Liquids  and  Solids  in  Grams  per  Cubic  Cen- 
timeter. 

-  CHAPTER   III 

ENERGY  AND  FORCE    .         .         .         .       -.         .         .         .  .      .       37 

Gravity.  —  Weight.  —  Center  of  Gravity.  —  Effect  of 
Air  on  Falling  Bodies.  —  Energy.  —  Inertia  and  Force.  — 
Centrifugal  Force.  —  Force  of  Expanding  Gases.  —  Molec- 
ular Forces.  —  Elasticity.  —  Cohesion  and  Adhesion.  — 
Shape  of  a  Free  Liquid.  —  Capillarity.  —  Diffusion.  — 
Osmosis. 

ix 


x  CONTENTS 

CHAPTER   IV 

PAGE 

MACHINES   .        ';        .        .        .        .        .         .        :..        .        .      53 

The  Evolution  of  Machines.  —  The  Principle  of  Work.  — 
The  Lever.  —  Classes  of  Levers.  —  Pulleys.  —  Wheel  and 
Axle.  —  The  Inclined  Plane.  —  The  Screw.  —  The  Wedge.  — 
Mechanical  Advantage.  —  Efficiency  in  Machines.  —  Power. 

—  Unit  of  Power.  —  Water  Power.  —  The  Overshot  Wheel. 

—  The  Undershot  Wheel.  —  The  Water  Turbine.  —  Wind 
Power.  —  The    Aeroplane.  —  The    Steam    Engine.  —  The 
Steam  Turbine.  —  Gasoline  Engines. 

CHAPTER    V 

THE  ATMOSPHERE       ,         .      .  .'        .         .         „        ,         .         .       73 

Weight  of  the  Atmosphere.  —  Air  Pressure.  —  Changes 
in  Atmospheric  Pressure  Due  to  Elevation.  —  The  Common 
Pump.  —  The  Force  Pump.  —  The  Centrifugal  Pump.  — 
The  Siphon.  —  Compressed  Air.  —  Oxygen.  —  Oxygen  and 
Ljfe.  —  Nitrogen.  —  Air,  a  Mixture.  —  Respiration.  —  The 
Lungs.  —  The  Air  Passages.  —  Mechanism  of  Breathing.  — 
Mouth  Breathing.  —  Adenoids.  —  Colds. 


CHAPTER   VI 

WATER      -   .         .         .         .         ,         .         .         .         ...       93 

Electrolysis  of  Water.  —  Water  by  Synthesis.  —  Physical 
and  Chemical  Changes.  —  Preparation  of  Hydrogen.  — 
Properties  of  Hydrogen.  —  Three  States  of  Water.  — 
Freezing  of  Water.  —  Steam.  —  Solutions.  —  Properties  of 
Solutions.  —  Water  of  Crystallization.  —  Evaporation.  — 
Evaporation,  a  Cooling  Process. 

CHAPTER   VII 

USES  OF  WATER          .     ' .     108 

Manufacture  of  Ice.  —  Cold  Storage.  —  Occurrence  of 
Water  in  Nature.  —  Water  Pressure.  —  Water  Pressure  on 
the  Sides  of  a  Tank.  -  -  Transmission  of  Pressure  by 
Liquids.  —  The  Hydraulic  Press.  —  Artesian  Wells.  — 
Archimedes'  Principle.  —  Submarines.  —  Density  of  a  Solid 


CONTENTS  xi 

PAGE 

Heavier  Than  Water.  —  Density  of  Solids  Lighter  Than 
Water.  —  Common  Uses  of  Water. —  Hardness  of  Water. 
—  Purification  of  Water.  —  City  Water  Supply. 


CHAPTER   VIII 

HEAT.     V.        Y        ,'     .         ,        .,  ...>'  .     .'       .        ...     .     126 

Sources  of  Heat.  —  Heat  by  Friction.  —  Heat  by  Com- 
pression. —  Heat    from    Chemical    Action.  —  The    Sun.  — 
Measurement     of     Temperature.  —  Effects     of     Heat.  — 
Expansion.  — r-  Expansion  of  Liquids.  —  Expansion  of  Gases. 
—  Fusion.  —  Vaporization.  —  Boiling.  —  Relation  of  Boil- 
ing Point  to  Pressure.  —  Laws  of  Ebullition. 

CHAPTER   IX 

QUANTITY  OF  HEAT  AND  TRANSMISSION  OF  HEAT     .         .         .     137 

The  Calorie.  —  Heat  Capacity.  — -  Latent  Heat.  —  Trans- 
I     ference  of  Heat.  —  Conductivity  of  the  Earth.  —  Conduc- 
tivity and  Sensation.  —  The  Fireless  Cooker.  —  The  Thermos 
Bottle.  —  The  Davy  Safety  Lamp.  —  Convection  in  Liquids. 
—  Convection  in  Gases.  —  Radiation.  —  Heating  and  Ven-  | 
tilating  of  Buildings.  — -  Hot-air  Heating.  —  Hot-water  Heat-  A 
ing.  —  The  Thermostat.  —  Ventilation.  —  Need  of  Moisture  ) 
in  the  Air. 


CHAPTER   X 

WEATHER    .         .     '  \     .   ..:    Y        ,         .         .         .         .         .     152 

Meaning  of  the  Term  "  Weather."    —  Functions  of  the  Air. 
—  Colors  of  the  Atmosphere.  —  Air  Density.  —  Isobars.  — 
Atmospheric     Temperature.  —  The     Thermograph.  —  Iso- 
therms. —  Change   of   Temperature    with    the    Seasons.  — 
Movements  of  the  Atmosphere.  — -  Terrestrial  or  Planetary 
Winds.  —  Trade     Winds.  —  Prevailing     Westerlies.  —  Cy- 
clonic Winds.  —  Hurricanes.  —  Winds  with  Special  Names. 
—  Monsoons.  —  Humidity  and  Precipitation.  —  The  Dew 
Point.  —  Dew  and  Frost.  —  Clouds.  —  Cumulus  Clouds.  — 
Cirrus  Clouds.  —  Stratus   Clouds.  —  Rainfall.  —  Thunder- 
storms. —  Weather  Changes.  —  The  W^eather  Bureau. 


xii  CONTENTS 

CHAPTER   XI 

PAGE 

MAGNETISM  AND  ELECTRICITY 186 

Magnets.  —  Law  of  Magnetic  Poles.  —  Induced  Magnet- 
ism. —  Nature  of  Magnetism.  —  Magnetic  Condition  of 
the  Earth.  —  The  Dipping  Needle.  —  Electrification  by 
Friction.  —  Two  Kinds  of  Electricity.  —  Conductors  and 
Insulators.  —  Theory  of  Electricity.  —  Charging  a  Body  by 
Induction.  —  Storing  a  Charge  of  Electricity.  —  Condensers. 
-  The  Leyden  Jar.  —  The  Electrophorus.  —  Atmospheric 
Electricity.  —  Current  Electricity.  —  Kinds  of  Cells  for 
Producing  Electricity.  —  Effects  of  Electric  Currents.  — 
Heating  Effects.  —  Table  of  Resistances.  —  Electric  Light- 
ing. —  Magnetic  Effects  of  Currents.  —  The  Electromagnet. 

—  The  Electric  Bell.  —  The  Telegraph.  —  The  Telephone. 

—  Chemical  Effects  of  Electricity.  —  Electrolysis.  —  Elec- 
troplating. —  The  Dynamo.  —  Electric  Motors. 


CHAPTER   XII 

SOUND          .         .         .         .         ;        V.         .         .         .         .212 

What  Causes  Sound.  —  Echoes.  —  Musical  Tones  and 
Noises.  —  Pitch.  —  Vibrating  Strings.  —  The  Voice.  —  The 
Hearing.  —  How  We  Hear. 


CHAPTER   XIII 

LIGHT  .        :'•.'        ,         . 220 

Light  and  its  Properties.  —  Sources  of  Light.  —  Lumi- 
nous Bodies.  —  Transparent,  Translucent,  and  Opaque 
Bodies.  —  Shadows.  —  Light  as  Energy.  —  How  Light  is 
Measured.  —  The  Bunsen  Photometer.  —  Reflection  of 
Light.  —  The  Reflection  of  Light  Compared  with  the  Reflec- 
tion of  Sound.  —  Diffused  or  Scattered  Light.  —  Refraction 
of  Light.  —  Lenses.  —  Uses  of  the  Lens.  —  The  Prism  and 
the  Composition  of  White  Light.  —  Length  of  Light  Waves. 

—  Absorption  of  Light  and  Color  Phenomena.  —  The  Sight. 

—  Protection  of  the  Eyes.  —  Structure  of  the  Eyeball.  — 
How  the   Eye   Does   its  Work.  —  Light  in  the  House.  — 
How  Glass  is  Made.  —  Artificial  Lighting.  —  The  Kerosene 


CONTENTS  xiii 


Lamp.  —  Gases  for  Lighting.  —  Natural  Gas.  —  Acetylene. 
—  Electric  Lighting.  —  Lighting  Fixtures. 


CHAPTER   XIV 

ELEMENTS,  COMPOUNDS,  AND  MIXTURES    .       ....         *         .         .     24(> 

Interrelation  of  the  Sciences.  —  How  Matter  is  Changed.  — 
Oxidation.  —  Elements,  Compounds,  and  Mixtures.  —  The 
Common  Elements.  —  Partial  List  of  Elements.  —  Metals. 
-  Iron.  —  Copper.  —  Mercury.  —  Sodium.  —  Silver.  - 
Gold.  — -  Chlorine.  —  Sulphur.  —  Carbon. 


CHAPTER   XV 

FUELS  AND  CARBON  COMPOUNDS        .         .  •      .         ."         .         .     259 

Fuels.  — Wood.  —  Coal.  —  Hydrocarbons.  —  Petroleum. 
—  Flash  Test.  —  Alcohols.  —  Sources  of  Fire.  —  Apparatus 
for  Utilizing  Fuels.  —  Stoves.  —  Carbon   Dioxide.  —  Prep- 
aration   of     Carbon     Dioxide.  —  Properties    and    Uses    of 
Carbon  Dioxide.  —  Fermentation.  —  Carbonates. 


CHAPTER   XVI 

COMMON  COMPOUNDS  OF  OTHER  ELEMENTS       ..         .         .         .     272 

Classes    of    Compounds.  —  Oxides.  —  Acids.  —  Uses    of 
Acids.  —  Alkalies  and  Bases.  —  Salts.  —  Uses  of  Salts.  — 
Electrolytes.  —  Analysis   of   Chemicals.  —  Iron.  —  Copper. 
—  Sodium.  —  Sulphates.  —  Chlorides. 

4 

CHAPTER   XVII 

SOILS  .         .         .     :    .         .         .         .       ...         .         .         .     280 

The  Crust  of  the  Earth.  —  Weathering.  —  How  Soil  is 
Made.  —  Glaciated  Soil.  —  Composition  of  Soils.  —  Table 
Showing  Mechanical  Analysis  of  Soils.  —  Names  of  Soils.  — 
Importance  of  the  Size  of  Soil  Particles.  —  Size  of  Soil 
Particles  in  Relation  to  Temperature  and  Crops.  —  Con- 
servation of  the  Soil.  —  Measure  of  Soil  Values.  —  Ferti- 
lizers. —  Nitrogen  as  a  Fertilizer.  —  Potassium  as  a  Ferti- 


xiv  CONTENTS 


lizer.  - —  Phosphorus  as  a  Fertilizer.  —  Lime   as  a  Fertilizer. 
-  How  to  Experiment  with  Fertilizer.  —  Why  We  Cultivate. 

—  Dry  Farming. 

CHAPTER   XVIII 

SURFACE  WATER,  DRAINAGE,  AND  IRRIGATION  .         .         .     299 

What  Becomes  of  the  Rainfall.  —  Ground  Water.  — 
Work  pf  Ground  Water.  —  River  Formation.  —  Lakes  and 
Inland  Seas.  —  Work  of  Rivers.  —  Erosion.  —  Deposition. 

—  Soil  Water.  —  Regulation  of  the  Amount  of  Soil  Water.  — 
Artificial  Drainage.  —  Irrigation. 


CHAPTER   XIX 

PLANTS       V.       '.;'...     .        .        .       .-. .     •.  •.        ..    ,     .         .         .     315 

Properties  of  Living  Matter.  —  The  Living  Plant.  —  Cells. 
-  Tissues.  —  Organs.  —  Multiplication  of  Cells.  —  Flowers. 
—  Pollination.  —  Fertilization.  —  Dispersal      of     Seeds.  — 
Germination      of      Seeds.  —  Roots.  —  Stems.  —  Leaves.  — 
Starch  Making  by  Leaves.  —  Digestion  in  Plants.  —  Flower- 
less     Plants.  —  Algae.  —  Fungi.  —  Mosses     and     Ferns.  — 
Distribution  of  Plants. 

CHAPTER   XX 

PLANTS  FROM  AN  ECONOMIC  STANDPOINT 335 

The  Value  of  Trees.  —  Trees  as  a  Protective  Covering  for 
the  Earth.  —  Uses  of  Wood.  —  Other  Uses  of  Trees.  —  Food 
Plants.  —  Textile    Plants.  —  Weeds.  —  Plant     Diseases.  — 
Wheat  Rust.  —  Brown  Rot.  —  Pear.  Blight.  —  Mildews.  - 
Potato    Scab.  —  Chestnut    Canker.  —  Molds.  —  Smuts.  —         *. 
Black  Knot.  —  Peach  Leaf  Curl.  —  Yeast. 


CHAPTER   XXI 

ANIMAL  LIFE .         .         .     350 

Relation  of  Plants  to  Animals.  —  One-celled  Animals, 
Amoeba.  —  Division  of  Labor.  —  Hydra.  —  Worms.  — 
Insects.  —  Bees  and  Ants.  —  Fishes.  —  Amphibians.  — 
Reptiles.  —  Birds.  —  Mammals.  —  Animals  Used  as  Food 


CONTENTS  XV 


—  Animal  Products  Used  for  Clothing.  —  Animals  which 
Aid    Man.  —  Animal    Pests.  —  Scale    Insects.  —  The    San 
Jose  Scale.  —  The  Codling  Moth.  —  The  Chinch  Bug.  - 
The  Hessian  Fly.  —  Poisons  for  Crop  Pests.  —  Stomachic 
Poisons.  —  Contact  Poisons. 

CHAPTER   XXII 

MAN'S  PLACE  IN  NATURE  .  .     372 

Man's  Place  among  the  Animals.  —  Language.  —  Man's 
Tools  and  Weapons.  —  The  Home. 

CHAPTER   XXIII 

FOODS  AND  NUTRITION       y       .  .     379 

Need  of  Food.  —  Bodily  Energy.  —  Measurement  of 
Food  Values.  —  Source  of  Food.  —  Food  Preservation  as 
Related  to  Food  Supply.  —  Transportation  as  Related  to 
Food  Supply.  —  The  Manufacturer's  Place  in  Food  Supply. 

—  Nature's  Food  Factories.  —  Kinds  of  Foods.  —  Proteins. 

—  Nitric  Acid  Test  for  Protein.  —  Biuret  Test  for  Protein.  — 
Carbohydrates.  —  Starch.  —  Glucoses.  —  Fehling's  Solution 
Test.  —  Sugars.  —  Fats.  —  Vitamines.  —  Ash  Constituents. 

-  Water.  —  Beverages.  —  Al'cohol.  —  Effects    of    Alcohol. 

—  How  Alcohol  is  Made.  —  Patent  Medicines.  —  Tobacco. 

-  Purchase  of  Food.  — The    Dietary.  —  Table    of    Food 
Values.  —  Principles  of  Cooking. 

CHAPTER   XXIV 

COMMUNITY  SANITATION      .         .         .         .         .         .         .  •       .     40fi 

Sanitation.  —  The  Growth  of  Cities.  —  Bacteria.  — 
Germs.  —  Source  of  Germs.  —  Conditions  Favorable  to 
Growth  of  Germs.  —  Resisting  Power  of  the  Body.  — 
Food  and  Disease.  —  Danger  in  Milk.  —  Preservatives.  — 
Danger  from  Water.  —  Public  Drinking  Cups,  Towels,  Etc. 

—  Street  Cleaning.  —  Garbage,  Ashes,  and  Rubbish.  —  Flies. 

—  Sewage  Disposal  and  Public  Health.  —  Typhoid  Fever.  — 
Colds.  —  Diphtheria.  —  Pneumonia.  —  Tuberculosis.  —  Scar- 
let  Fever.  —  Measles.  —  Smallpox.  —  Diseases  Carried  by 
Insects.  —  Malaria.  —  Yellow  Fever.  —  Quarantine.  —  Dis- 
infectants. —  Fumigation. 


The  36-inch  Telescope  of  Lick  Observatory. 


GENERAL   SCIENCE 


CHAPTER   I 
THE   EARTH 

The  Earth's  Relation  to  the  Universe.  —  The  ancients 
regarded  the  earth  as  the  center  of  the  universe  and  their 
conception  of  it  was  a  very  natural  one,  both  because 
of  its  importance  to  them  and  because  the  heavenly 
bodies  actually  appeared  to  revolve  about  the  earth  as 
a  center.  Men  saw  the  sun  rise  in  the  east  and  set  in 
the  west  every  day,  and  the  stars  appear  in  nearly  the 
same  positions  every  night.  Hence  they  concluded  that 
the  sun  and  stars  all  moved  around  the  earth  once  in 
twenty-four  hours. 

They  made  careful  observations,  mapped  out  the 
heavens,  and  recorded  the  positions  of  the  stars.  Grad- 
ually they  discovered  that  many  of  their  ideas  were 
wrong,  and  little  by  little  through  hundreds  of  years  the 
real  facts  have  become  known  concerning  the  vast  or- 
ganism which  we  call  the  universe. 

From  these  facts  we  find  that  the  earth  is  but  one  of 
a  number  of  similar  bodies  called  planets  and  is  not  at 
all  conspicuous  among  them.  It  is  neither  the  largest 
nor  the  smallest ;  the  farthest  from  nor  nearest  to  the 
suri.  If  we  were  to  view  it  from  some  distant  point, 
we  should  be  surprised  at  its  comparative  unimportance. 


2 :  ;  GENERAL  SCIENCE 


The  universe  of  which  we  are  so  small  a  part  is  made 
up  of  many  systems  of  heavenly  bodies.  These  systems 
probably  consist,  each  of  a  central  body  like  our  sun, 
around  which  revolve  planets  with  their  satellites, 
and  comets.  Many  of  these  systems  are  no  doubt 
much  larger  than  our  solar  system,  great  and  complex 
though  it  seems  to  us. 

The  Solar  System  —  so  called  from  the  Latin  word 
sol  meaning  sun  —  consists  of  the  sun  at  the  center,  the 
planets  and  their  satellites,  the  planetoids  or  asteroids, 
and  some  comets.  There  are  seven  other  planets  be- 
sides the  earth  revolving  around  the  sun.  They  have  no 
light  of  their  own  like  the  true  stars,  but  the  light  that 
comes  to  us  from  them  is  a  reflection  of  the  light  of  the 
sun.  If  we  carefully  observe  the  bright  points  of  light 
in  the  sky  at  night,  we  shall  see  that  the  true  stars  twinkle, 
while  the  planets,  when  they  are  visible,  give  a  steady 
light  like  that  of  the  moon. 

The  Planets.  -  -  The  names  of  the  planets  comprising 
the  solar  system,  beginning  with  the  one  nearest  the  sun, 
are:  Mercury,  Venus,  Earth,  Mars,  Jupiter,  Saturn, 
Uranus,  and  Neptune  (Figure  1).  Because  of  their  mo- 
tion around  the  sun  the  planets  are  continually  chang- 
ing their  positions  in  relation  to  the  other  stars,  whereas 
the  positions  of  the  true  stars  do  not  appear  to  change 
relatively  to  one  another.  It  is  due  to  this  change  of 
position  that  they  are  called  planets  —  from  the  Greek 
word  meaning  wanderer.  The  amount  of  time  required 
by  the  several  planets  to  make  a  revolution  about  the 
sun  of  course  varies  to  a  considerable  degree,  due  to  the 
great  difference  in  distance  which  they  have  to  travel. 
This  difference  in  time  of  revolution  accounts  for  their 
change  of  position  in  relation  to  each  other. 


THE  EARTH  3 

The  largest  of  the  planets  is  Jupiter,  which  is  more 
than  three  hundred  and  seventeen  times  as  large  as  the 
earth.  Saturn  is  next  smaller,  and  then  follow  in  order 
Neptune,  Uranus,  Earth,  Venus,  Mars,  and  Mercury. 

The  brightest  of  the  planets  are  Venus,  Mars,  Jupiter, 
and  Saturn,  and  they  are  plainly  visible  at  certain  periods. 


Neptune 


FIG.  .  1.  —  The  Sun  and  Planets. 


It  is  very  seldom  that  all  four  are  seen  at  the  same  time 
in  any  evening,  but  two  are  often  in  the  sky  together 
and  sometimes  three.  Part  of  the  time  they  are  morn- 
ing stars  and  at  other  times  evening  stars.  The  other 
three  planets  —  Mercury,  Uranus,  and  Neptune  —  can- 
not be  seen  easily  without  a  telescope. 

Satellites  or  Moons.  —  Not  only  do  the  planets  revolve 
around  the  sun,  but  each  of  them,  except  Mercury  and 


FIG.  2.  —  The  Planet  Saturn  and  Its  Rings. 


THE  EARTH  5 

Venus,  has  one  or  more  smaller  bodies  revolving  around 
it.  These  bodies  are  called  satellites  or  moons.  The 
earth  has  one  of  these  moons,  and  Saturn  has  the  greatest 
number,  ten  in  all.  In  addition  to  its  ten  satellites 
Saturn  has  several  concentric,  bright  rings  surrounding 
it  and  revolving  about  it  (Figure  2).  When  Saturn 
is  situated  so  as  to  show  the  broad  side  of  the  rings, - 


FIG.  3. 

once  in  fifteen  years,  —  it  is  in  its  brightest  phase  and  is 
a  wonderful  sight  through  the  telescope  (Figure  3). 

Planetoids  and  Comets.  —  Besides  the  planets  and 
their  satellites  there  are  in  the  solar  system  about  six 
hundred  planetoids  or  asteroids.  These  are  solid  bodies 
much  smaller  than  the  planets,  revolving  in  orbits  be- 
tween Mars  and  Jupiter.  Within  the  limits  of  the  solar 
system  are  also  comets  —  heavenly  bodies  consisting 
of  a  head,  with  a  very  bright  spot  gradually  shading  into 
a  less  luminous  portion,  and  a  tail  or  streamer  (Figure  4). 
Some  of  the  comets  seem  to  have  regular  paths  about  the 
sun,  making  their  appearance  at  regular  intervals,  and 
must  be  considered  a  part  of  the  solar  system;  others 
appear  as  occasional  visitors,  never  to  return. 


GENERAL  SCIENCE 


FIG.  4.  —  A  Comet. 

Stars.  —  When  we  observe  the  heavens  at  night,  the 
stars  seem  to  be  innumerable,  but  it  is  not  strictly  true 
to  say  that  the  number  actually  visible  to  us  is  countless. 
There  are  only  about  7000  stars  bright  enough  to  be  seen 
with  the  naked  eye  under  perfect  conditions,  that  is,  on  a 
clear,  moonless  night  with  the  atmosphere  free  from  dust 


THE  EARTH 


FIG.  5.  — The  Milky  Way. 

and  vapor.  Owing  to  the  presence  of  dust  and  vapor, 
however,  the  number  of  stars  in  the  whole  sky  that  can 
readily  be  seen  is  only  about  2500.  With  the  largest  tele- 
scope about  one  hundred  million  may  be  seen  (Figure  5). 


8  GENERAL  SCIENCE 

As  we  have  said  before,  the  true  stars  shine  with  a 
twinkling  light  as  distinguished  from  the  steady  light 
of  the  planets ;  most  of  the  fixed  stars  are  suns  like  ours 
-  many  of  them  much  larger  —  with  their  own  systems 
of  planets.  We  can  readily  understand  how  very  large 
and  luminous  they  must  be  when  we  learn  that,  although 
the  nearest  fixed  star  is  millions  of  millions  of  miles  away, 
yet  we  can  see  it  and  observe  its  brilliance,  even  though 
it  takes  three  and  one  half  years  for  its  light  to  reach 
us,  traveling  at  the  enormous  speed  of  186,000  miles  a 
second. 

Constellations.  —  Certain  groups  of  bright  stars  near 
together  are  known  as  constellations.  Most  of  them 
were  traced  and  given  their  names  long  ago  by  the  com- 
mon people  —  shepherds  and  sailors,  who  lived  much 
out  of  doors  with  nothing  to  aid  them  in  their  study  of 
the  heavens  but  their  own  eyes  and  fancy. 

Of  the  ancient  constellations  there  are  about  forty- 
eight.  All  are  outlined  by  stars  that  may  be  seen  with 
the  naked  eye,  for  they  were  discovered  long  before  the 
invention  of  the  telescope.  Their  names  have  been  given 
from  some  fancied  resemblance  to  an  ancient  hero,  an 
animal,  or  an  object.  Most  of  them  do  not  much  resemble 
the  thing  for  which  they  are  named  and  in  this  respect 
prove  rather  disappointing.  On  the  whole  they  are 
mere  abstractions  bounded  by  certain  imaginary  and 
by  no  means  definite  lines.  Many  of  them  overlap  each 
other. 

The  North  Star.  —  If  we  look  in  the  northern  part  of 
the  sky,  we  may  see  a  group  of  seven  stars  which  outline 
the  form  of  a  long-handled  dipper.  This  group  is  known 
as  the  "  Big  Dipper  "  and  is  a  part  of  a  larger  constel- 
lation called  the  Great  Bear  (  Ursa  Major).  The  two 


THE  EARTH 


9 


stars  on  the  side  of  the  bowl  farther  from  the  handle 
are  called  the  "  pointers  "  because  an  imaginary  line 
drawn  through  them  and  extended  for  five  times  the 
distance  between  them  will  end  almost  exactly  at  the 
North  Star  or  Pole  Star.  The  Pole  Star  (Polaris)  is 
so  called  because  the  imaginary  'axis  of  the  earth,  if  ex- 
tended from  the  north 
pole,  would  pierce  the 
sky  very  near  this 
star  (Figure  6). 

The  circle  of  stars 
in  the  northern  sky 
seems  to  revolve 
about  this  Pole  Star, 
just  as  all  the  lands 
of  the  terrestrial 
globe  seem  to  revolve 
around  the  north  pole 
as  the  globe  is  ro- 
tated. The  stars  in 
this  northern  circle 


THE  DIPPER 


_  ,  -  -     North  Star 


complete  their  small 
round  once  in  twenty- 
four  hours,  moving  in 

a     direction     Opposite   FlG-  6- — Diagram  showing  the  Position  of  the 
, ,          ,  i  -  North  Star  in  the  Sky. 

to   the    hands    of    a 

clock  (Figure  7).  As  the  path  of  the  northern  circle  of 
stars  lies  entirely  above  the  horizon,  they  never  rise  or 
set,  but  are  only  obscured  by  the  light  of  day.  They 
are  visible  on  any  clear  night  in  the  year  from  all  points 
in  the  northern  hemisphere. 

Six   well-defined    constellations    are   included   in   this 
northern  circle,  and  they  are  always  above  the  horizon. 


10 


GENERAL  SCIENCE 


in  our  latitude.  They  are :  The  Big  Dipper,  the  Little 
Dipper  or  Little  Bear  ( Ursa  Minor),  of  which  the  North 
Star  forms  the  end  of  the  handle  or  tail,  Draco  or  the 
dragon,  Cassiopeia  (in  her  chair),  Cepheus,  the  royal 
husband  of  Cassiopeia,  and  Perseus  (Figure  8). 

Next  below  the  northern  circle  comes  a  line  or  belt  of 
stars  describing  a  larger  circle  around  the  pole.     These 
...-,  stars  lie  below  the 

horizon  for  a  longer 
or  shorter  time,  de- 
pending on  .their 
position  in  relation 
to  the  pole.  They 
rise  in  the  north- 
east, make  a  long 
slow  sweep  of  the 
sky,  and  set  in  the 
northwest,  finish- 
ing their  circle  be- 
low the  horizon. 
There  is  another 
belt  of  stars  that 
rises  somewhere 
near  the  exact  east- 


North 


Summer 


Autumn 


Spring 


Star  Winter 


FIG.  7. 


Positions  of   the   Dipper  in  Relation  to 
the  North  Star. 


Seen  in  the  early  evening  at  the  seasons  named. 

ern  point  of  the  horizon,  crosses  the  heavens  to  the  western 
point  in  about  twelve  hours,  and  remains  below  the  hori- 
zon for  another  twelve  hpurs.  The  stars  in  those  circles 
which  lie  farther  and  farther  south  of  us  never  rise  very 
high  in  the  heavens,  only  very  small  portions  of  these 
circles  being  visible  to  us. 

Some  of  the  most  important  constellations  in  these 
latter  belts  of  stars  are:  Orion,  Hercules,  Taurus,  Scor- 
pius,  and  Cam's  Major.  In  the  last-named  constellation 


THE  EARTH 


11 


is  Sirius  the  "  Dog  Star,"   which  when  visible  is  the 
brightest  star  in  the  whole  sky. 

The  change  in  the  position  of  stars  which  can  be  ob- 
served from  hour  to  hour  is  caused  by  the  rotation  of 
the  earth  on  its 
axis,  and  the 
change  in  position 
apparent  from 
month  to  month 
is  caused  by  the 
revolution  of  the 
earth  around  the 
sun.  The  appar- 
ent motion  of  the 
stars  is  always 
westward,  because 
the  earth's  motion 
on  its  axis  and 
around  the  sun  is 
from  west  to  east. 

The  Moon.  -  -  The  earth  has  one  satellite,  the  moon, 
which  revolves  around  it  once  a  month  (27.32  days) 
and  accompanies  it  through  space  in  its  journey  around 
the  sun.  The  diameter  of  the  moon  is  about  2163 
miles  and  its  distance  from  the  earth  is  about  240,000 
miles.  Although  we  see  the  moon  as  a  very  bright 
object  at  night  for  a  part  of  every  month,  yet  it  has 
no  light  of  its  own  but  shines  entirely  by  reflected 
light  from  the  sun  (Figure  9).  It  has  a  rough,  barren, 
rocky  surface  and  as  far  as  is  known  has  no  air  or 
water  upon  it.  While  the  moon  makes  one  journey 
around  the  earth,  it  rotates  only  once  on  its  axis/ 
Because  the  moon's  period  of  rotation  is  the  same  as 


FIG.  8.  —  Constellations  in  the  Northern  Sky. 


12  GENERAL  SCIENCE 

its  period  of  revolution,  it  always  turns  the  same  side 
toward  the  earth. 

Phases  of  the  Moon. --When  the  moon  is  in  that 
part  of  its  orbit  nearest  the  sun,  it  is  almost  between 


FIG.  9.  —  The  Moon. 
Photographed  at  the  Lick  Observatory. 

the  earth  and  the  sun.  The  side  illuminated  is  then 
turned  away  from  the  earth  and  we  see  but  a  mere  fringe 
of  illumination,  a  thin  crescent.  We  call  this  phase  the 


THE   EARTH 


IS 


"  new  moon  " 


(Figure  10).  When  it  has  completed  a 
fourth  of  its  journey,  we  see  one  half  of  its'  illuminated 
surface  or  one  fourth  of  its  total  surface ;  this  is  the 
"  first  quarter."  When  it  has  completed  half  its  circuit 
and  is  on  the  opposite  side  of  the  earth  from  the  sun, 
we  see  half  of  its  total  surface  or  its  whole  illuminated 
surface ;  it  is  then  "  full  moon.'7  When  it  is  at  the  third 

— >    --0-- 


Sun's        /~l 
~_7iays  . 


Earth 


-o- 

FIG.    10.  —  Phases  of  the  Moon. 

quarter,  we  again  see  one  fourth  of  its  total  surface  or 
one  half  its  illuminated  surface. 

The  moon  rises  about  fifty  minutes  later  each  day 
than  on  the  previous  day.  It  has  moved  eastward 
from  the  place  where  it  was  the  day  before,  and  so  the 
earth  must  turn  a  little  farther  on  its  axis  before  the 
moon  comes  into  view  at  the  horizon. 

The  Sun.  —  The  sun  is  the  center  of,  and  by  far  the 
largest  and  most  important  body  in,  the  solar  system. 
All  the  planets  of  the  system  revolve  about  it  and  receive 


14 


GENERAL  SCIENCE 


heat  and  light  from  it.  It  has  a  diameter  of  866,000 
miles  and  is  much  larger  than  all  the  other  planets  com- 
bined. If  the  earth  were  placed  at  its  center,  thei^  would 
be  room  for  the  moon  to  revolve  in  its  regular  orbit, 

which  would  still  be 
200,000  miles  from 
the  circumference  of 
the  sun  (Figure  11). 
The  reason  for  the 
extremely  hot  con- 
dition of  the  sun 
is  not  known.  Its 
interior  is  thought 
to  be  composed  of 
a  dense  white-hot 
liquid,  and  the  outer 
portions  are  known 
to  be  intensely 
heated  gases  (Fig- 

FIG.  11.  —  Diagram  Showing  Comparative  Sizes  .  . 

of   the   Earth,   the    Orbit  of   the  Moon,  and   the     Ure    12).        1  he    SUn 

is  composed  of  the 

same  elements  .as  the  earth,  but  its  condition  is  so  hot 
that  these  elements  can  be  recognized  only  by  means  of 
the  spectroscope,  an  instrument  used  in  the  study  of  light. 
Shape  of  the  Earth.  —  Children,  if  they  are  concerned 
with  the  question  at  all,  imagine  that  the  earth  is  a  flat 
place  bounded  by  a  few  hills  or  a  quantity  of  water, 
according  to  where  they  live ;  they  are  concerned  with 
no  people  other  than  those  in  their  immediate  locality 
and  those  that  they  see  in  their  very  limited  travels. 
In  the  childhood  of  the  race,  people  in  general  held  the 
same  ideas.  They  imagined  the  earth  as  flat,  and  in 
sailing  their  crude  vessels  were  careful  not  to  venture 


THE  EARTH 


15 


too  far  from  land  for  fear  of  encountering  strange  mon- 
sters or  falling  over  the  "  edge  "  of  the  earth. 

The    great    Greek    philosopher,    Aristotle,    who    lived 
about  the  middle  of  the  fourth  century  B.C.,  observed 


FIG.  12.  —  Flames  on  the  Edge  of  the  Sun. 

the  curved  outline  of  the  earth's  shadow  on  the  moon 
at  the  time  of  an  eclipse  and  concluded  from  this  observa- 
tion that  the  earth  must  have  a  curved  surface  like  a 
globe.  About  the  beginning  of  the  Christian  Era,  writers 
began  to  refer  to  the  argument  for  the  curvature  of  the 
earth  based  on  the  disappearance  of  the  lower  part  of 
a  vessel  when  sailing  out  to  sea  (Figure  13) ;  that  fact 


FIG.  13.  —  Showing  the  Curvature  of  the  Earth. 

had  evidently  been  noted  by  many  for  some  time  pre- 
vious. 

The  knowledge  thus  gained  by  the  wise  men  of  the 
ancient   Mediterranean   countries   concerning  the  shape 


16 


GENERAL  SCIENCE 


of  the  earth  was  unknown  to  the  rest  of  the  world  and 
afterwards  forgotten.  Not  until  about  the  time  of 
Columbus  was  it  regained,  and  since  that  time  many 
people  have  sailed  around  the  earth.  Wonderful  dis- 
coveries have  been  made  concerning  the  earth,  and  almost 
every  part  of  its  surface  has  been  explored. 

Men   who   have   made   careful   measurements   of   the 
shape  of  the  earth  tell  us  that  it  is  an  oblate  spheroid, 

that  is,  a  sphere  which 
is  somewhat  flattened  at 
two  opposite  points.  An 
orange  is  an  oblate  sphe- 
roid, but  the  flattening  of 
an  orange  is  much  greater 
in  proportion  to  its  di- 


FIG.  14.  —  The  Earth  is  an  Oblate  Spheroid. 


ameter  than  is  that  of 
the  earth  (Figure  14). 
The  polar  diameter  of 
the  earth  is  only  twenty- 
seven  miles  shorter  than 
the  equatorial  diameter, 
and  twenty-seven  miles 
is  a  very  small  amount  when  compared  to  the  average 
diameter  of  the  earth,  which  is  about  8000  miles. 

When  we  look  at  the  very  high  mountains  on  the  sur- 
face of  the  earth  and  think  of  the  depressions  on  the  floor 
of  the  ocean,  which  are  more  than  five  miles  deep,  we 
wonder  how  a  body  with  such  great  irregularities  can  be 
called  a  sphere  at  all.  However,  we  must  remember 
that  this  notion  is  due  to  our  nearness  of  view,  and  that, 
when  compared  to  the  great  size  of  the  whole  earth, 
these  irregularities  are  less,  in  proportion,  than  the  slight 
ridges  on  the  surface  of  the  orange. 


THE  EARTH  17 

Cause  of  the  Shape  of  the  Earth.  —  Gravitation  tends 
to  make  a  mass  spherical  in  shape.  This  result  is  ac- 
complished more  readily  if  the  mass  is  plastic  and  elastic, 
which  the  earth  is  to  a  slight  extent,  although  it  seems 
very  firm  and  rigid  to  us.  In  addition  to  the  effect 
which  gravitation  has,  there 
is  also  the  effect  of  rotation, 
which  causes  the  slight  ob- 
lateness  or  flatness  at  the 
poles.  The  particles  of  a 
rotating  body  tend  to  fly  off 
in  straight  lines  tangent  to  FIG  15 

the   direction  in  which   the 

body  is  rotating,  and  this  tendency  would  cause  an 
accumulation  of  the  earth's  material  at  the  equator  and 
the  loss  of  it  at  the  poles. 

If  a  metal  hoop  which  is  free  to  move  along  its  axis 
is  rotated  on  a  whirling  table,  this  effect  of  centrifugal 
force  will  be  well  illustrated  (Figure  15). 

Size  of  the  Earth.  -  -  The  earliest  recorded  estimate 
of  the  size  of  the  earth  was  made  by  a  Greek  philosopher 
in  the  third  century  B.C.  He  reckoned  it  to  be  about 
8111  miles  in  diameter,  arriving  at  this  conclusion  through 
measurements  taken  on  the  surface  of  the  earth.  The 
actual  polar  diameter  as  discovered  later  is  7899  miles, 
and  the  equatorial  diameter  is  7926  miles. 

Consequences  of  the  Shape  and  Size  of  the  Earth.  — 
The  great  size  of  the  earth  and  the  irregularities  of  its 
surface  have  affected  the  distribution  and  growth  of 
peoples,  animals,  and  plants  to  a  remarkable  degree. 
The  great  distances  between  tribes,  and  the  almost  in- 
surmountable barriers  in  the  form  of  mountains,  oceans, 
and  deserts^  for  centuries  hindered  the  mingling  of  tribes 


18  GENERAL  SCIENCE 

and  caused  marked  differences  in  their  customs  and  lan- 
guages. The  same  barriers  confined  animals  and  plants 
to  certain  localities,  thus  fostering  and  developing  their 
peculiar  characteristics. 

The  advancement  of  science,  the  invention  of  various 
means  of  travel  and  communication,  and  the  progress 
of  civilization  have  done  much  toward  overcoming  these 
natural  barriers,  so  that  now  the  earth  may  be  considered 
a  relatively  small  body,  with  almost  every  portion  of  its 
surface  accessible  to  the  active  traveler. 

Structure  of  the  Earth.  —  For  convenience  of  study, 
the  earth  is  divided  into  several  parts  or  spheres  :  (1)  the 
outer,  gaseous  envelope,  or  atmosphere;  (2)  the  liquid 
envelope,  the  water  or  hydrosphere;  (3)  the  solid  rocky 
part,  the  lithosphere;  (4)  the  center,  the  nucleus  or 
centrosphere. 

Motions  of  the  Earth.  —  The  earth  has  three  motions, 
two  of  which  greatly  influence  all  things  living  upon  it. 
The  first  is  a  daily  motion,  or  rotation  on  its  axis;  the 
second  is  a  yearly  motion,  or  revolution  about  the  sun; 
the  third,  which  is  usually  disregarded  because  of  its 
lack  of  noticeable  effects,  consists  of  an  onward  motion 
through  space  which  the  earth  has,  together  with  the 
other  parts  of  the  solar  system. 

Rotation.  -  -  The  earth  turns  once  on  its  axis  every 
twenty-four  hours  (Figure  16).  As  this  rotation  takes 
place,  the  sun  is  shining  upon  one  half  of  the  earth's 
surface,  leaving  the  other  half  in  darkness.  The  effect 
to  us  is  that  of  the  sun  rising  at  one  point  in  the  horizon, 
moving  over  the  sky,  and  setting  at  some  point  in  the 
horizon  nearly  opposite.  In  reality  we  are  being  turned 
into  and  out  of  the  sunlight.  The  same  effect  is  noticed 
when  riding  on  a  swiftly  moving  train.  The  train  seems 


THE  EARTH 


19 


DAY 


to  be  standing  still  while  the  objects  along  the  track 
whirl  by. 

The  succession  of  day  and  night,  which  is  caused  by 
the  rotation  of  the  earth,  has  given  man  and  many  ani- 
mals the  habit  of 
working  in  the 
light  and  resting 
in  the  darkness. 
Rotation  is  also 
one  of  the  factors 
along  with  others 
in  producing  tides, 
influencing  certain 
belts  of  winds  and 
calms,  affecting 
the  direction  of 
ocean  currents, 
and  causing  the 
flattening  of  the 
earth  at  the 
poles. 

Directions.  —  We  say  down  when  we  mean  toward 
the  center  of  the  earth  and  up  for  the  opposite  direction. 
In  addition  to  these  the  rotation  of  the  earth  suggests 
a  natural  system  of  directions  by  which  the  relative 
positions  of  different  places  may  be  indicated.  Toward 
the  North  Pole  on  the  surface  of  the  earth  is  north; 
toward  the  South  Pole  is  south.  The  direction  in  which 
the  sun  "  rises"  we  call  east;  that  in  which  it  "sets  "'is 
west.  However,  the  true  east  and  west  line,  at  any  place, 
is  always  at  right  angles  to  the  north  and  south  line. 

The  Celestial  Meridian.  —  An  imaginary  line  called 
the  celestial  meridian  is  also  an  important  factor  in  the 


FIG.  16.  —  The  Succession  of   Day  and  Night 
Caused  by  the  Rotation  of  the  Earth. 


20 


GENERAL  SCIENCE 


location  of  places  and  the  reckoning  of  time.  This  line 
is  a  circle  which  passes  through  the  north  point  of  the 
horizon,  the  zenith  —  the  portion  of  the  sky  directly 
over  one's  head  —  the  south  point  on  the  horizon,  and 
extends  around  the  other  side  of  the  earth  to  the  north 
point  again. 

It  divides  the  sky  into  an  east  and  a  west  half.  When 
the  sun  or  moon  crosses  the  meridian  (mid-day  line), 
it  has  made  half  its  daily  journey  from  rising  to  setting. 
The  abbreviations  A.M.  and  P.M.  refer  to  the  time  when 
the  sun  crosses  the  meridian,  being  taken  from  the  Latin 
phrases,  ante  meridiem  and  post  meridiem.  Since  this 
NORTH  imaginary  circle 

passes  through  the 
zenith,  there  is  a 
celestial  meridian 
for  every  ob- 
server. 

»  Meridians  and 
Parallels.  -  -  For 
purposes  of  cal- 
culating distance 
and  time,  imag- 
inary lines  are 
drawn  on  the 
earth's  surface  ex- 
tending from  pole  to  pole.  These  lines  are  at  certain 
intervals  and  lie  on  the  earth  directly  under  the  celestial 
meridian  of  the  places  through  which  they  run.  They 
are  numbered  east  and  west,  so  many  degrees  from  the 
prime  meridian,  or  the  meridian  of  0°.  This  meridian 
passes  through  Greenwich,  England  (Figure  17). 

Running   at   right   angles    to    the   meridians   are   the 


SOUTH 

FIG.  17.  —  Parallels  and  Meridians. 


THE   EARTH 


21 


parallels,  or  imaginary  lines  running  around  the  earth 
parallel  to  the  equator,  which  is  the  largest  of  these 
circles  and  is  considered  as  0°.  The  other  parallels 
are  numbered  so  many  degrees  north  or  south  of  the 
equator. 

Latitude  and  Longitude.  — .The  distance  north  or 
south  of  the  equator  is  called  latitude  and  is  measured 
in  degrees  on  the  meridians  by  the  parallels.  Distance 
east  and  west  of  the  prime  meridian  is  called  longitude 
and  is  measured  in  degrees  on  the  parallels  by  the  me- 
ridians. 

Local  Time.  —  The  period  of  the  earth's  rotation 
furnishes  a  natural  unit  of  time,  the  day,  easily  recog- 
nized and  everywhere  constant. 
Before  there,  were  any  clocks, 
people  told  the  time  of  day  by 
the  sundial  (Figure  18).  This 
consisted  of  a  vertical  rod,  the 
shadow  of  which  fell  on  a  hori- 
zontal plane.  From  noon  or  the 
time  when  the  sun  cast  the 
shortest  shadow  on  one  day 
until  it  cast  the  shortest  shadow 
on  the  next  day  was  considered 
a  day's  time  or  a  solar  day,  and 
was  divided  into  twenty-four 
hours.  Before  the  advent  of 
railroads  and  the  telegraph,  each 
community  used  the  mean  solar 
time  of  its  own  meridian. 

Standard  Time.  —  When  railways  extending  east  and 
west  became  numerous  in  the  United  States,  it  became 
very  inconvenient  to  use  local  time,  for  the  traveler 


FIG.  18. —  Sundial. 


22 


GENERAL  SCIENCE 


found  his  timepiece'  always  too  fast  or  too  slow  according 
to  the  direction  in  which  he  journeyed.  To  avoid  this 
confusion  the  American  Railway  Association  in  1883 
persuaded  the  government  to  adopt  standard  time. 

By  this  plan  the  United  States  is  divided  into  four 
time  sections,  or  belts.  .Certain  meridians  15°  apart  in 
longitude  and  one  hour  apart  in  time  are  taken  as 


FIG.  19.  —  Standard  Time  Belts  in  the  United  States. 

standard.  Each  belt  uses  the  mean  solar  time  of  its 
standard  meridian.  Only  the  middle  of  the  belt  has 
the  true  time  by  the  sun ;  other  parts  of  the  belt  differ 
from  the  sun's  time  in  periods  of  from  one  to  thirty 
minutes. 

The  names  of  the  four  time  belts  are  the  Eastern, 
Central,  Mountain,  and  Pacific,  each  extending  for  ap- 
proximately 7£°  on  each  side  of  the  meridians  numbered 
respectively  75°,  90°,  105°,  and  120°  west  of  Greenwich 


THE  EARTH  23 

(Figure  19).  Everywhere  in  a  given  belt  the  clocks 
are  an  hour  ahead  of  those  in  the  next  belt  west  and  an 
hour  behind  those  in  the  next  belt  east.  When  it  is  noon 
at  New  York,  it  is  11  A.M.  in  Chicage,  10  A.M.  in  Denver, 
and  9  A.M.  at  San  Francisco.  The  accurate  standard 
time  is  sent  once  a  day  at  twelve  o'clock,  by  telegraph, 
from  the  Naval  Observatory  at  Washington  to  all  cities 
in  the  United  States.  By  electric  connection  many  clocks 
are  thus  set  exactly  right  each  day. 

Revolution  of  the  Earth.  —  The  earth  moves  once 
around  the  sun  in  365J  days.  The  path  in  which  it  travels 
is  elliptical  in  shape  and  is  called  its  orbit.  The  revolu- 
tion of  the  earth  around  the  sun  gives  us  our  measure 
of  time  called  a  year  and  causes  the  sun  to  appear  to 
shift  its  position  in  the  heavens  from  day  to  day. 

The  axis  of  the  earth  constantly  points  in  the  same 
direction  whatever  its  position  in  its  orbit.  The  axis 
is  inclined  to  the  plane  of  that  orbit  66|°  or  23^°  from 
the  perpendicular.  This  inclination  of  the  axis  causes  the 
earth  to  assume  quite  different  positions  with  reference 
to  the  sun  at  different  times  of  the  year.  To  this  is  due 
the  varying  lengths  of  day  and  night  and  the  change  of 
seasons. 

Change  of  Seasons.  —  From  spring  to  autumn  when 
the  north  pole  is  inclined  toward  the  sun  (Figure  20), 
the  sun's  rays  are  received  vertically  at  places  in  the  torrid 
zone  north  of  the  equator  and  obliquely  at  places  within 
a  distance  of  90°  north  of  the  torrid  zone.  During  this 
time  the  sun's  rays  cover  the  north  pole  continuously, 
causing  the  very  long  days  in  the  frigid  zone.  It  is  then 
summer  in  the  northern  hemisphere,  the  days  being 
longer  and  warmer  there  than  in  the  southern  hemi- 
sphere, because  the  rays  of  the  sun  are  more  nearly 


24  GENERAL  SCIENCE 

vertical  over  that  whole  portion  of  the  globe.  On  the 
twenty-first  of  June  the  rays  of  the  sun  fall  vertically 
on  the  Tropic  of  Cancer,  23  i°  north  of  the  equator.  The 
sun  has  now  reached  its  farthest  point  north,  the  days 
being  longest  and  nights  shortest  at  this  time  in  the 
frigid  and  temperate  zones. 

From  autumn  to  spring  the  north  pole  is  turned  away 
from  the  sun.     It  is  then  winter  in  the  northern  latitudes, 


SPRING 


sunriER 


AUTUMN 
FIG.  20.  —  Change  of  Seasons. 

and  the  days  are  shorter  and  colder  than  in  the  southern 
latitudes.  On  December  twenty-first  the  sun  reaches 
its  most  southern  point,  the  direct  rays  falling  on  the 
Tropic  of  Capricorn,  23  J°  south  of  the  equator.  In 
its  apparent  moving  from  the  Tropic  of  Cancer  to  the 
Tropic  of  Capricorn  and  back,  the  sun  seems  to  cross 
the  equator  twice,  the  vertical  rays  falling  on  that  imagi- 
nary line  about  March  twenty-first  and  September 
twenty-third. 


THE  EARTH  25 

QUESTIONS 

1.  Why  do  we  see  no  stars  in  the  day  time?     How  may 
planets  be  distinguished  from  true  stars? 

2.  What  planets  are  visible  to  the  naked  eye?     What  planets 
have  no  satellites? 

3.  How  often   does   Halley's   Comet   make  its   appearance? 
When  did  it  last  appear  ? 

4.  Name  two  constellations  that  are  visible  on  any  clear  night 
in  the  northern  hemisphere.     Why  is  the  Pole  Star  so  called? 

5.  How  many  rotations  does  the  earth  make  while  the  moon 
is  making  one? 

6.  Does  the  moon  have  day  and  night?     What  is  the  length 
of  a  "  day  "  on  the  moon? 

7.  What  simple  proofs  are  there  that  the  earth  is  round? 

8.  What  proportion  of  the  earth's  diameter  is  the  height  of 
the  highest  mountain? 

9.  If  a  man  left  Havana,  Cuba,  about  June  twenty-first  and 
traveled  slowly  to  Rio  Janeiro,  reaching  there  about  December 
twenty-first,  what  changes  of  season  would  he  experience? 

10.  What  part  of  the  earth's  surface  is  illuminated  by  the  sun 
at  one  time?     Why  does  the  lighted  space  move  to  the  westward? 
How  many  degrees  per  hour  does  it  move? 

11.  If  the  sun  rises  at  7  A.M.  at  places  on  the  75th  meridian 
west  longitude,  at  what  meridian  will  it  rise  an  hour  later  ? 

12.  When  it  is  eight  o'clock  at  Philadelphia,  what  time  is  it  in 
St.  Louis?     Pittsburg?     Los  Angeles?     Detroit?     Cleveland? 


CHAPTER  II 
MATTER  AND   ITS   PROPERTIES 

OUR  previous  study  of  geography  has  given  us  some 
ideas  of  the  material  or  matter  of  which  the  world  is  com- 
posed. Matter  is  defined  as  anything  which  occupies 
space.  A  substance  is  any  particular  kind  of  matter. 
The  earth  is  composed  of  many  different  substances  — 
rocks  and  soils,  water,  air,  and  various  forms  of  animal  life 
that  use  the  soil,  the  water,  and  the  air  to  sustain  their 
lives. 

Matter  exists  in  three  different  forms,  namely :  solids, 
liquids,  and  gases,  and  all  the  substances  of  the  earth  exist 
in  one  or  more  of  these  forms.  Many  solids  may  be 
changed  to  liquids  by  the  application  of  heat.  Metals 
are  the  best  examples  of  this  phenomenon.  Water  exists 
in  all  three  states,  solid,  liquid,  and  gaseous ;  as  ice,  water, 
and  steam. 

A  solid  has  a  definite  volume  and  a  definite  shape,  as  a 
stone  or  a  piece  of  wood.  A  liquid  has  definite  volume, 
but  the  shape  is  that  of  the  containing  vessel.  A  gas  has 
neither  definite  volume  nor  definite  shape,  but  expands 
indefinitely  as  the  pressure  on  it  decreases. 

Constitution  of  Matter.  —  To  know  that  a  certain  sub- 
stance is  called  wood,  and  that  one  article  is  made  of  glass 
while  another  is  made  of  iron,  is  not  enough  to  satisfy  the 
inquiring  mind.  We  want  to  know  what  these  substances 
are  composed  of. 

26 


MATTER  AND   ITS  PROPERTIES  27 

While  man  has  succeeded  in  combining  a  number  of 
elements,  or  fundamental  substances,  in  supposedly  new 
ways  to  form  many  new  compounds,  yet  all  these  sub- 
stances that  man  has  been  working  with  have  existed 
in  some  form  since  the  very  beginning  of  time.  We 
have  found  a  number  of  elemental  things  on  the  earth, 
but  the  number  is  not  so  large  as  might  be  supposed,  for 
while  we  have  several  hundred  thousand  different  com- 
pound substances  they  are  all  composed  of  combinations 
of  about  eighty  elements. 

A  few  of  these  fundamental  substances  are  well  known 
to  us,  such  as  iron,  lead,  zinc,  copper,  tin,  aluminum, 
mercury,  nickel,  silver,  gold,  and  platinum  among  the 
metals ;  oxygen,  hydrogen,  and  nitrogen  among  the  gases, 
and  carbon,  which  does  not  belong  with  either  the  metals 
or  the  gases.  Our  bodies  are  composed  chiefly  of  carbon 
and  three  of  these  gases — oxygen,  hydrogen,  and  nitrogen. 

We  might  think  at  first  that  if  we  knew  the  properties 
of  each  of  the  elements,  it  would  be  quite  easy  to  predict 
the  properties  of  each  of  the  compounds  of  these  same  ele- 
ments. This,  however,  is  far  from  being  the  case.  As  the 
elements  combine,  they  lose  their  individuality  entirely. 
For  example,  if  we  combine  oxygen  and  hydrogen,  two 
gases,  we  have  water,  very  different  in  appearance  and 
different  in  all  its  properties  (cf.  p.  94). 

Just  how  the  elements  differ  from  one  another  is  hard 
to  tell.  All  the  elements  are  composed  of  extremely 
small  particles,  called  atoms.  Atoms  are  so  very  small 
that  they  cannot  be  seen  with  the  most  powerful  micro- 
scopes that  have  been  made.  There  are  just  as  many 
different  kinds  of  atoms  as  there  are  elemental  substances. 
We  use  a  different  term  to  designate  the  particles  formed 
when  two  or  more  of  these  atoms  unite.  We  do  not 


28  GENERAL  SCIENCE 

speak  of  an  atom  of  water,  for  the  smallest  particle  of 
water  that  can  exist  is  composed  of  one  atom  of  oxygen 
combined  with  two  atoms  of  hydrogen.  This  combina- 
tion of  atoms  we  call  a  molecule  of  water.  A  molecule 
is  the  smallest  particle  of  water  that  can  possibly  exist; 
for  if  the  atoms  of  oxygen  and  hydrogen  are  separated, 
we  no  longer  have  water  but  the  two  elements  in  the 
form  of  gases. 

Molecules  are  usually  composed  of  atoms  of  different 
kinds ;  the  atoms  may  be  all  of  one  kind,  however.  The 
molecules  of  some  substances  are  composed  of  a  large 
number  of  atoms  of  different  kinds.  The  molecule  of 
alum  is  composed  of  at  least  one  hundred  atoms.  In 
our  work  on  electricity  we  shall  have  something  more 
to  say  about  atoms  and  the  way  they  are  held  together. 

Properties  of  Matter.  —  With  so  many  different  people 
in  the  world  it  would  seem  at  first  impossible  to  dis- 
tinguish the  individuals.  However,  our  experience  has 
shown  us  that  with  all  the  millions  of  human  beings  there 
are  always  individual  characteristics  or  properties  which 
enable  us  to  tell  one  from  another.  It  is  the  same  way 
with  the  substances  which  go  to  make  up  the  earth. 

Those  characteristics  or  properties  which  are  held  in 
common  by  all  substances  are  called  general  properties, 
and  those  properties  which  belong  only  to  certain  kinds 
of  matter  and  enable  us  to  distinguish  one  substance 
from  another  are  called  special  properties. 

All  matter  occupies  space  to  the  exclusion  of  all  other 
matter  from  that  same  space. 

Experiment  i.  —  Fit  a  two-hole  rubber  stopper  to  a  pint  bottle 
(Figure  21).  Through  one  hole  of  the  stopper  pass  a  funnel 
tube  and  through  the  other  pass  a  delivery  tube  leading  to  a  bowl 
of  water.  Pour  water  into  the  funnel  tube.  What  causes  the 


MATTER  AND   ITS   PROPERTIES 


29 


bubbles  in  the  bowl  of  water?     Now  close  the  delivery  tube  and 

pour  more  water  into  the  funnel  tube.     Does  the  water  go  into 

the   bottle   as   before?     Is   air   matter?      In   this   respect   air  is 

like  all  other  matter. 

Air,     however,     has 

other    properties 

which  enable  us   to 

distinguish    it    from 

other  gases,  such  as 

hydrogen  or  carbon 

dioxide. 

Other  examples  of 
general  properties  of 
matter  are  weight, 
inertia,  and  porosity.  FIG.  21. 


We  can  easily  tell  salt  from  sugar  by  the  taste.  If  we 
examine  a  piece  of  chalk  and  a  piece  of  iron,  we  find  tha,t 
the  chalk  is  more  brittle  than  the  iron.  The  iron  is  also 
quite  heavy  and  will  scratch  a  stone,  while  the  chalk  is 
light  and  will  leave  a  white  mark  on  the  stone.  Glass 
and  wood  have  quite  different  properties.  Glass  is  heavier 
than  water,  transparent,  brittle,  and  very  hard.  Wood 
on  the  other  hand  is  lighter  than  water,  opaque,  not 
so  brittle  as  glass,  and  so  soft  that  it  may  be  cut  easily 
with  a  knife.  These  properties  are  special  properties, 
and  we  might  make  a  long  list  of  them,  for  there  are 
enough  to  enable  us  to  distinguish  all  the  thousands  of 
substances  that  are  known.  Many  of  these  properties 
are  relative,  as  we  may  have  observed  from  the  illustra- 
tions given  above.  We  say  that  a  substance  is  harder 
than  another,  or  that  it  is  more  elastic,  or  that  its  color 
is  a  deeper  shade  of  red,  and  thus  by  comparison  dis- 
tinguish one  substance  from  another. 

Measurement.  —  It  is  necessary  in  our  discussion  of 


30  GENERAL  SCIENCE 

matter  and  space  to  agree  on  certain  standards  by  which 
they  shall  be  measured.  There  have  been  such  standards 
used  by  all  the  civilized  nations,  but  they  have  been  of 
various  values.  For  example,  the  unit  of  length  corre- 
sponding to  the  English  foot  has  had  different  lengths 


FIG.  22. —  Standard  Yard  Bar. 

in  different  countries.  This  unit  was  usually  derived 
from  the  supposed  average  length  of  the  human  foot. 
In  England,  the  yard  was  finally  established  as  the 
standard  unit  of  length  and  was  supposed  to  represent 
the  length  of  the  arm  of  Henry  the  First,  but  later  the 
standard  was  more  definitely  fixed  and  is  now  the  length 
of  a  metal  bar  kept  in  London  (Figure  22).  The  United 
States  uses  the  same  standard,  a  .copy  of  the  standard 


Courtesy  of  Bureau  of  Standards,  Washington,  D.C. 
FIG.  23. —  United  States  National  Prototype  Meter  Bar. 

yard  being  kept  at  our  Capitol.  The  foot  was  arbi- 
trarily taken  as  one  third  of  the  yard,  and  the  other  units 
were  derived  in  the  same  way.  There  are  12  inches  in 
a  foot,  3  feet  in  a  yard,  5J  yards  or  16|  feet  in  a  rod,  and 
320  rods  in  a  mile. 


MATTER  AND   ITS   PROPERTIES  31 

It  will  be  seen  that  there  is  very  little  relation  between 
these  different  numbers  and  that  some  of  them  are  dif- 
ficult to  use  as  multipliers.  This  led  the  people  of  Europe 
to  adopt  a  different  system  of  measurements  known  as 
the  metric  system. 

The  Metric  System.  —  At  the  time  of  the  French 
Revolution  a  commission  was  appointed  in  France  to 


1 

~r~r 

I  '  J 

•  Centimeters 

J 

J 

J" 

X 

Inches 

FIG.  24.  —  Comparison  of  the  Centimeter  with  the  Inch. 

devise  a  system  of  measurements  which  would  do  away 
with  the  existing  confusion  arising  from  the  use  of  so 
many  different  standards  in  different  localities.  The 
system  was  adopted  in 
France  in  1793  and  has 
since  been  adopted  by  the 
governments  of  nearly  all 
the  large  nations  except 
England  and  the  United  ~ 
States.  In  science,  how- 
ever, it  is  USed  even  by  FIG.  25.  — Relative  Size  of  Kilogram  and 

these  nations.  Pound  Weights- 

The  meter  is  the  standard  unit  of  length  of  the  metric 
system.  It  is  the  distance  between  two  transverse  lines 
ruled  on  a  bar  of  platinum  which  is  kept  in  the  palace  of  the 
Archives  in  Paris  (Figure  23) .  The  Government  of  France 
has  made  a  number  of  copies  of  this  bar  and  distributed 
them  among  the  principal  governments  of  the  world.  Two 
of  them  are  kept  in  the  Capitol  of  the  United  States  at 


32  GENERAL  SCIENCE 

Washington.  The  length  of  the  meter  in  terms  of  the 
English  system  is  39.37  inches  (Figure  24). 

The  standard  unit  of  volume  of  the  metric  system  is  the 
liter.  It  is  the  volume  of  a  cube  each  edge  of  which  is 
one  tenth  of  a  meter.  The  liter  is  a  little  larger  than  a 
quart,  being  equivalent  to  1.057  quarts. 

The  standard  unit  of  weight  of  the  metric  system  is  the 
kilogram  (Figures  25-26).  The  kilogram  is  the  weight  of 


Courtesy  of  Bureau  of  Standards,  Washington,  D.C. 
FIG.  26. —  United  States  National  Prototype  Kilogram. 

a  liter  of  water  of  4°  Centigrade  or  39.20°  Fahrenheit. 
Since  the  standard  meter  has  been  measured  in  terms 
of  light  waves  and  the  other  standards  are  defined  in 
terms  of  the  standard  meter,  it  would  now  be  possible  to 
make  new  standards  if  those  which  now  exist  should  be 
destroyed. 

Metric  Tables 

LENGTH 

10  millimeters  (mm.)  =  1  centimeter 
10  centimeters  (cm.)    =  1  decimeter 
10  decimeters   (dm.)    =  1  meter 
1000  meters      (m.)      =  1  kilometer 


MATTER  AND   ITS   PROPERTIES  33 

SURFACE  MEASUREMENT 
100  square  millimeters  =  1  square  centimeter 
100  square  centimeters  =  1  square  decimeter 
100  square  decimeters    =  1  square  meter 
100  square  meters          =  1  are 

CUBIC  MEASURE 

1000  cubic  millimeters  (c.mm.)  =  1  cubic  centimeter 
1000  cubic  centimeters  (c.c.)      =  1  cubic  decimeter 
1000  cubic  decimeters  (c.dm.)    =  1  cubic  meter 

WEIGHT 

10  milligrams  (mg.)    =  1  centigram 
10  centigrams  (eg.)     =  1  decigram 
10  decigrams    (dg.)     =  1  gram 
1000  grams       (g.)       =1  kilogram 
1000  kilograms  (kg).   =-1  metric  ton 

TABLE  OF  ENGLISH  EQUIVALENTS 
1  meter          =  39.37  inches,  or  3.28  feet 
1  liter  =  1.057  quarts 

1  kilogram     =  2.2046  pounds 
1  metric  ton  =  2204.6  pounds 

A  little  study  will  convince  us  that  the  metric  system 
has  some  advantages  over  other  systems.  It  is  a  decimal 
system  throughout  and  can  be  used  just  as  our  decimal 
system  of  coinage  is  used.  For  example,  we  may  write 
five  dollars,  three  dimes,  and  five  cents  as  $5.35 ;  five 
meters,  two  decimeters,  one  centimeter,  and  three  milli- 
meters may  be  written  5.213  meters. 

The  Measurement  of  Length.  —  All  measurements  of 
length  are  simply  the  comparison  of  the  length  of  the  ob- 
ject with  some  standard.  If  the  measurement  is  to  be 
taken  in  the  metric  system,  the  comparison  is  with  the 
standard  meter  bar  ;  if  by  the  English  system,  the  compari- 
son is  with  the  standard  yard  at  London. 


34  GENERAL  SCIENCE 

The  Measurement  of  Volume.  —  All  bodies  have  three 
dimensions,  and  if  the  shape  of  the  body  to  be  measured 
is  regular,  it  will  be  easy  to  measure  the  length,  breadth, 
and  thickness  and  compute  the  volume.  If  the  solid  is 
irregular,  it  is  necessary  to  use  other  means  in  determining 
the  volume  of  space  it  occupies.  When  a  solid  is  immersed 
in  a  liquid,  it  displaces  its  own  volume  of  the  liquid,  and 
this  means  may  be  used  in  determining  the  volume  of 
such  solids  as  cannot  be  accurately  measured.  Can  you 
devise  a  method  of  determining  the  volume  of  a  solid  which 
floats  in  water  ? 

Experiment  2.  —  Determine  the  volume  of  a  cylinder  of  wood  by 
first  measuring  it  with  a  ruler  and  then  by  the  displacement  method. 
How  do  the  two  determinations  compare  ? 

Measurement  of  Mass.  —  Mass  must  not  be  confused 
with  volume.  The  measurement  of  mass  simply  means 

that  we  shall  de- 
termine the  weight 
of  an  object  by 
comparing  it  with 
some  standard.  We 
are  able  to  detect 
differences  in  weight 
by  our  muscular 
sense  if  the  differ- 
ences  are  great 

FIG.  27. —  Common  Tip  Scales  or  Balances. 

enough,     but      we 

should  not  care  to  rely  upon  the  judgment  of  the  grocer 
who  sold  his  sugar  by  weight  as  estimated  by  his  muscles. 
For  this  work  a  balance  is  used  (Figure  27).  If  the  arms 
of  the  balance  are  of  equal  length,  the  weights  used  must 
be  as  heavy  as  the  object  to  be  weighed.  The  object  to 
be  weighed  is  then  placed  on  one  side  and  the  weights 


MATTER  AND   ITS  PROPERTIES 


35 


are  placed  on  the  other  side.  The  sum  of  the  weights 
necessary  to  balance  the  beam  is  the  weight  of  the  object. 
For  heavier  masses  a  system  of  levers  is  used,  as  in  a 
platform  scale  where  the  weights 
used  are  fractional  multiples  of  the 
reading  on  the  scale  beam. 

Density  and  Specific  Gravity.  - 
Since  equal  volumes  of  different  sub- 
stances such  as  iron,  wood,  lead, 
aluminum,  and  granite  do  not  have 
the  same  mass  or  weight,  we  use  the 
term  density  to  indicate  the  differ- 
ences in  the  weights  of  definite  vol- 
umes of  these  various  substances. 
Before  we  are  very  old  we  learn  that 
some  substances  are  heavier  than 
others.  A  piece  of  iron  is  heavier 
than  a  piece  of  wood  of  the  same 
size,  and  we  say  that  the  density  of 
iron  is  greater  than  that  of  wood. 

To  get  the  maSS  Of  a  body  We  Weigh   the.  determination  of  small 
,  11-  T    •  i      weights. 

it  and  to  get  the  density  we  divide 
its  weight  in  grams  by  its  volume  in  cubic  centimeters. 
Density  determined  by  this  procedure  also  gives  the 
numerical  value  of  the  specific  gravity  of  the  substance. 
Specific  gravity  is  the  ratio  of  the  weight  of  a  substance 
to  the  weight  of  an  equal  volume  of  water. 


FIG.  28.  — The  Spring 

Balance. 
Quite  commonly  used  in 


Density 
Specific  gravity  = 


mass  m  grams 
volume  in  c.c. 

weight  of  body 


weight  of  equal  volume  of  water 

Density  in  grams  per  cubic  centimeter  is  specific  grav- 
ity, but  density  in  terms  of  any  other  system  of  weights 


36  GENERAL  SCIENCE 

and  measures  will   not   correspond   numerically  to   the 
specific    gravity. 

A  cubic  foot  of  water  weighs  62.3  pounds  or  about 
1000  ounces,  while  by  definition  a  .cubic  centimeter  of 
water  weighs  one  gram. 

Densities  of  Liquids  and  Solids  in  Grams  per  Cubic 
Centimeter 

LIQUIDS 

Alcohol '     .79       Hydrochloric  acid  .     .    ...      1.27 

Glycerine 1.26       Mercury.       .    ..  '  .     .     .     13.6 

SOLIDS 

Aluminum     ......   2.58  Lead 11.3 

Brass    . 8.5  Pine 5 

Copper      .     .     .     .     .     .    .  8.9  Platinum 21.5 

Cork     .     ....     .     .         .25  Silver .     .  10.53 

Glass 2.6  Tin 7.29 

Gold 19.3  Zinc 7.15 

Iron  (cast)     .....       7.4 

QUESTIONS  AND  PROBLEMS 

1.  A  tank  is  2  feet  deep,  3  feet  wide,  and  5  feet  long.     What 
weight  in  pounds  of  water  can  it  hold  ? 

2.  A  rectangular  block  of  iron  is  10  cm.  long,  4  cm.  deep,  and  3  cm. 
wide  and  weighs  888  grams.     What  is  the  density  of  the  iron? 

3.  Find  the  weight  of  5  cubic  centimeters  of  glycerine. 

4.  How  does  a  molecule  differ  from  an  atom? 

5.  Name  ten  special  properties  of  matter. 

6.  In  what  respects  does  a  liquid  differ  from  a  gas? 

7.  Make  a  list  of  properties  of  the  following  substances :  chalk, 
glass,  coal,  lead,  and  salt. 

8.  Why  should  a  barrel  have  a  vent  hole  in  it  ? 

9.  How  does  iron  differ  from  copper? 

10.  Do  you  see  any  advantages  of  the  metric  system  over  the 
English  system? 

11.  What  difficulties  would  there  be  in  changing  from  our  system 
to  the  metric  system  for  all  measurements? 


CHAPTER   III 
ENERGY  AND   FORCE 

ENERGY  appears  in  so  many  different  forms  and  its 
changes  from  one  form  to  another  are  made  so  rapidly, 
that  it  is  sometimes  hard  for  us  to  believe  that  we  are 
dealing  with  varied  forms  of  the  same  thing. 

The  usual  definition  of  energy  is  capacity  for  doing 
work,  and  we  say  that  work  is  done  when  force  acts 
through  space.  The  words  energy  and  force  are  often 
misused  for  each  other  in  ordinary  speech,  but  in 
science  these  two  words  have  distinctive  meanings. 
Force  is  any  cause  which  alters  a  body's  state  of  rest 
or  of  uniform  motion  in  a  straight  line.  It  requires  force 
to  stop  a  moving  body  just  as  it  requires  force  to  set  it 
in  motion  when  it  is  in  a  state  of  rest.  Considerable 
force  must  be  exerted  by  a  team  of  horses  to  start  in  motion 
a  loaded  wagon.  After  it  is  started,  however,  just  as 
much  force  must  be  exerted  to  stop  it,  but  the  force  nec- 
essary to  stop  it  will  not  all  need  to  come  from  the  horses. 
There  is  another  force  at  work  which  causes  the  wagon 
to  rub  very  hard  on  the  surface  over  which  it  passes. 
This  force  is  called  gravity  or  the  force  of  gravitation. 

Gravity.  —  Sir  Isaac  Newton  (1642-1727)  first  an- 
nounced the  law  which  we  now  call  the  law  of  gravitation, 
although  it  is  now  quite  certain  that  the  much  abused 
Galileo  had  a  very  definite  knowledge  concerning  this 
force.  The  law  states  that  every  body  in  the  universe 
attracts  every  other  body  with  a  force  which  varies 

37 


38  GENERAL  SCIENCE 

inversely  as  the  square  of  the  distance  between  the  two 
bodies  and  which  varies  directly  as  the  product  of  the 
masses  of  the  two  bodies.  Newton  formulated  the  law  in 
order  to  account  for  the  fact  that  the  earth  pulls  bodies 
toward  it  and  also  to  account  for  the  maintenance  of  the 
planets  and  their  satellites  in  their  respective  orbits. 

We  know  that  objects  which  are  free  to  fall  do  fall 
to  the  earth,  and  probably  most  of  us  would  be  willing 
—    to  accept  this  without  question,  because 
we  become  so  accustomed  to  this  force  that 
the  question  "  why  "  might  never  occur  to 
us.     It  is  not  easy  to  imagine  this  great 
force.     It  acts  through  space,  but  there 
are    no  attachments  between    the  bodies 
attracted.     The  apple  on  the  tree  is  exert- 
ing a  pull  on  the  earth  just  as  the  earth  is 
exerting  a  pull  on  the  apple.     Whenever 
the  force  which  holds  the  stem  of  the  apple 
to  the  tree  is  less  than  the  pull  of  the  earth, 
the  apple  falls  to  the  ground.     Why  does 
not  the  earth  seem  to  fall  to  the  apple  ? 
If  two  balls,  one  quite  large  and  the  other  small,  are 
hung  side  by  side  (Figure  29)  the  small  ball  will  be  drawn 
toward  the  large  one  and  the  supporting  cord  will  no  longer 
hang  plumb. 

When  we  say  that  the  law  of  gravitation  is  universal, 
we  simply  mean  that  it  applies  to  all  the  matter  of  the 
universe.  It  exists  between  the  earth,  sun,  moon,  and 
stars  as  well  as  between  the  objects  which  are  so  near  us. 
Weight.  — Weight  is  simply  the  measure  of  the  force 
of  gravitation  on  any  particular  mass  or  quantity  of 
matter.  The  quantity  of  matter  in  a  body  is  the  mass 
of  the  body.  In  the  last  chapter  we  learned  that  the 


ENERGY  AND  FORCE 


39 


gram  is  the  unit  of  mass  in  the  study  of  science,  although 
we  are  accustomed  to  think  of  mass  in  terms  of  pounds 
of  the  English  system.  The  attraction,  or  pull,  that  the 
earth  exerts  on  a  given  mass  is  irrespective  of  the  kind 
of  matter  in  the  body.  The  pull  on  a  pound  of  feathers 
is  the  same  as  the  pull  on  a  pound  of  lead. 

Center  of  Gravity.  —  A  large  body  such  as  a  block  of 
stone  is  made  up  of  countless  small  particles  of  matter. 
Now  according  to  our  law  of 
gravitation,  each  little  particle 
of  matter  attracts  and  will  be 
attracted  by  the  others  and  by 

,,  ,,          T         ,,  i      ,-u  FIG.  30.  —  Center  of  Gravity 

the  earth.     In  other  words  there   or  Center  of  Mass  of  a  Complex 
will  be  a  countless   number  of   Form- 
little  pulls  between  these  particles  of  matter  in  the  stone 
and  the  earth,  and  it  is  evident  that  the  sum  of  these  little 
pulls  between  the  particles  and  the  earth  will  equal  the 

total  pull  of  the  earth  on  that 
body.  The  point  in  a  body  at 
which  a  single  force  equal  in 
magnitude  to  the  weight  of  the 
body  and  directed  upward  can 
be  applied  so  that  the  body  will 
remain  at  rest  in  whatever  posi- 
tion it  is  placed  is  called  the 
center  of  gravity.  It  is  the 
place  at  which  all  the  weight 
may  be  said  to  be.  To  do  this 
mechanically  we  simply  find  a 
place  at  which  the  body  will 

FIG.  31 .  —  Determining  the  Center    1 

of  Gravity.  balance  (Figure  30). 

Experiment  3.  —  The  center  of  gravity  of  a  piece  of  uniformly  rolled 
metal  may  be  found  in  the  following  manner.     Support  it  from  one 


40  GENERAL  SCIENCE 

corner  by  a  pin  stuck  through  a  hole  near  its  edge.  Hang  a  plumb 
line  from  the  pin  and  draw  a  line  ba  (Figure  31)  parallel  to  and 
directly  under  the  plumb  line.  Now  hang  the  piece  of  metal  from 
another  point  c  and  draw  another  line  cd  in  the  same  way  that  the 
line  ab  was  drawn.  The  intersection  of  these jtwo  lines  will  be  the 
center  of  gravity  of  the  piece  of  metal.  It  should  balance  at  this 
point,  and  if  a  needle  is  passed  through  a  hole  made  at  this  point, 
the  metal  should  remain  at  rest  in  whatever  position  it  is  placed. 

The  center  of  gravity  of  the  earth  is  somewhere  near 
the  geometrical  center  of  it.  The  pull  of  the  earth  for 
mathematical  purposes  may  be  considered  to  be  at  that 
point.  Now  an  object  at  the  poles  is  about  thirteen 
miles  nearer  to  the  center  of  the  earth  than  an  object 
at  the  equator,  and  as  a  consequence  an  object  will  weigh 
more  at  the  poles,  the  difference  being  about  one  part 
in  590.  What  will  be  the  effect  on  the  weight  of  objects 
of  taking  them  up  in  the  air  several  miles  ? 

Objects  are  said  to  be  in  "  stable  "  or  "  unstable  " 
equilibrium  according  to  the  position  of  the  center  of 


FIG.  32.  — Stable  and  Unstable  Equilibrium. 

gravity  of  the  mass  (Figure  32).  An  object  is  in  its  most 
stable  position  when  its  center  of  gravity  is  as  low  as 
possible.  In  what  position  will  a  sphere  be  in  most  stable 
equilibrium?  A  cylinder?  A  cone? 

Effect  of  Air  on  Falling  Bodies.  —  A  stone  and  a  feather, 
if  dropped  from  the  top  of  a  tall  building,  will  not  reach 
the  earth  in  the  same  time.  The  reason  is  that  the  air 
resists  being  pushed  out  of  the  way,  and  the  heavier 
object  more  easily  overcomes  this  resistance.  If  the  air 


ENERGY  AND  FORCE 


41 


is  exhausted  from  a  tube  arranged  for  the  purpose,  it 
will  be  found  that  the  feather  will  fall  as  rapidly  as  the 
stone,  because  it  is  not  influenced  by  the  resist- 
ance of  the  air  (Figure  33). 

Energy.  —  It  is  quite  easy  for  us  to  realize 
that  energy  may  be  transferred  from  one  body  to 
another.  A  moving  billiard  ball  strikes  another 
ball  "  full,"  and  apparently  all  of  its  energy  is 
immediately  transferred  to  the  second  ball,  while 
the  first  ball  stops.  In  fact,  however,  not  quite  all 
the  energy  of  the  first  ball  was  transferred  to  the 
second.  Part  of  it  went  into  other  forms  of  energy, 
as  heat  and  sound.  The  billiard  ball  in  motion 
possesses  energy  of  motion.  The  name  which 
scientists  have  given  this  form  of  energy  is  kinetic 
energy,  a  name  derived  from  the  Greek 
word  kineo,  moving.  In  recent  years 
we  have  had  a  new  word  from  this  FlG-33- 
root,  kinematograph  or  cinematograph.  Ki- 
netic energy  is  one  of  the  several  distinct 
forms  of  energy  which  we  shall  learn  about 
in  our  work  in  science. 

We  may  pull  a  stone  away  from  the  earth, 
and  the  earth  pulls  it  back  again.  If,-  however, 
we  pull  the  stone  away  from  the  earth  and 
support  it  there,  the  stone  will  have  the  power 
of  doing  work  when  it  is  freed.  This  form 
of  energy  is  called  potential  energy.  There 
are  numerous  instances  of  such  energy.  The 
weights  of  a  clock  when  lifted  possess  potential 
energy  (Figure  34).  Confined  steam  furnishes 
another  example.  It  is  the  energy  of  strain  or  deforma- 
tion as  well  as  the  energy  due  to  position.  Potential 


FIG.  34. 


42  GENERAL  SCIENCE 

energy  until  released  is  valueless.  It  is  simply  because 
it  can  readily  be  transformed  into  kinetic  energy  that  we 
think  of  it  as  energy.  Although  there  are  several  distinct 
forms  of  energy,  all  energy  is  either  kinetic  or  potential. 
The  capacity  for  doing  work  can  be  possessed  only  by 
a  body  already  in  motion  or  by  one  held  under  some  sort 
of  strain.  Other  forms  of  energy  are  chemical  energy, 
light  energy,  heat  energy,  and  electrical  energy. 

Inertia  and  Force.  —  All  matter  has  a  tendency  to 
continue  in  its  state  of  rest  or  motion.     If  it  is  at  rest, 

force  is  required  to 
put  it  in  motion, 
and  when  it  is  in 
motion,  force  is  re- 
quired to  bring  it 
to  rest  again  or 
even  to  change  its 
rate  of  motion. 
This  tendency  of 
matter  to  continue 

m   a    Stat°    ° 


FIG.  35.  —  Illustration  of  Inertia.     The  inertia  of 
the  coin  causes  it  to  remain  on  the  fingers  when    or   motion   W6    Call 
B  card  is  snapped  away.  inertia  (Figure35)  § 

We  have  often  noticed  this  tendency,  but  we  have  never 
heard  its  name.  As  the  street  car  starts,  the  people  who 
are  standing  are  thrown  backward  and  as  it  stops  sud- 
denly they  are  thrown  forward.  This  is  on  account  of 
the  inertia  of  their  bodies.  A  loaded  wagon  requires 
more  force  to  start  it  in  motion  than  to  keep  it  in  motion 
when  once  started,  and  if  it  is  moving  on  a  level  pave- 
ment, it  requires  considerable  force  in  addition  to  that 
exerted  by  gravity  to  bring  it  to  a  stop.  The  direction 
of  the  motion  is  always  in  a  straight  line  or  simply  a 


ENERGY  AND   FORCE  43 

continuation  of  motion  at  any  particular  instant.  When 
mud  is  thrown  from  a  rapidly  rotating  carriage  wheel, 
it  does  not  follow  the  curve  of  the  wheel,  but  flies  off  in 
a  straight  line  with  the  direction  in  which  it  was  going 
when  it  left  the  wheel.  The  same  phenomenon  is  noticed 
when  a  sling  is  rotated  (Figure  , 

36)  and  suddenly  released.    The          $'*""        *"X 
weighted  sling  goes  in  a  straight 
line  which  is  tangent  to  the  circle      // 
in  which  it  was  rotating. 

Centrifugal  Force. — The  force 
which  caused  the  sling  to  pull  so 
hard  on  the  hand  is  centrifugal  \  /] 

force  or  center  fleeing  force.     It     "-•  :*v:^  ,.S 

is  the  same  force  which  causes     FlG.  36. -Centrifugal  Force, 
the  water  to  stay  in  a  rotating 

bucket.  It  is  not  a  new  force  but  a  name  given  to  this 
particular  manifestation  of  inertia.  It  is  the  force  which 
sometimes  causes  emery  wheels  to  burst,  which  enables 
us  to  separate  the  milk  from  the  cream  in  the  separator 
by  causing  the  milk  to  move  farther  out  than  the  lighter 
cream,  and  which  makes  the  equatorial  diameter  of  the 
earth  greater  than  the  polar  diameter. 

At  the  beginning  of  this  chapter  we  said  it  would  be 
necessary  to  think  of  force  and  energy  as  having  distinct 
meanings.  There  are  a  number  of  forces  with  which  we 
are  in  almost  daily  contact :  gravitational  force  ;  muscu- 
lar force,  such  as  that  exerted  by  man  and  beasts  of 
burden;  the  force  of  the  wind;  the  force  of  expanding 
gases  ;  and  others  which  are  not  so  common. 

Muscular  force  is  a  force  which  will  always  be  used. 
Even  if  beasts  of  burden  should  no  longer  be  needed, 
muscular  force  exerted  by  man  will  always  be  a  neces- 


44  GENERAL  SCIENCE 

sity.  Our  very  existence  depends  on  it.  Our  health 
requires  it. 

It  is  necessary  to  take  into  account  the  element  of  time 
in  calculating  the  amount  of  work  done  by  a  force.  If 
one  horse  can  do  a  piece  of  work  in  one  hour  and  it  re- 
quires three  hours  for  another  to  do  the  same  work,  there 
is  a  great  difference  in  their  rate  of  doing  work.  This 
rate  of  doing  work  is  called  power.  James  Watt  (1736- 
1819),  who  invented  the  steam  engine,  thought  that  the 
average  horse  could  do  33,000  foot  pounds  of  work  per 
minute;  that  is,  raise  33,000  pounds  one  foot  in  one 
minute  or  550  pounds  one  foot  in  one  second.  While 
this  number  is  probably  too  high,  it  has  been  taken  as 
the  unit  of  power  in  English-speaking  countries  and  has 
been  named  the  horse  power  (H.P.).  Steam  engines 
and  motors  are  usually  rated  in  horse  power. 

Force  of  Expanding  Gases.  —  There  are  a  number  of 
ways  in  which  the  force  of  expanding  gas  does  work. 
The  steam  engine  is  simply  a  device  for  utilizing  the 
energy  of  steam.  When  steam  is  produced  under  high 
pressure  and  confined,  it  is  potential  energy,  but  when 
it  is  allowed  to  expand  in  a  cylinder,  the  energy  is  used 
to  produce  motion  which  may  be  employed  in  various 
ways  (Figure  37). 

In  the  gasoline  engine,  the  energy  is  set  free  by  the 
explosion  of  gasoline  vapor  and  air.  This  explosion 
produces  a  large  volume  of  gases,  the  expansion  of  which 
causes  the  piston  to  move,  as  in  a  steam  engine. 

The  efficiency  of  modern  war  engines,  some  of  which 
throw  immense  shells  to  a  distance  of  twenty-five  miles, 
is  due  to  the  production  of  compounds  which  explode 
with  the  evolution  of  large  quantities  of  gases.  With 
these  explosives  it  is  necessary  that  the  energy  should 


ENERGY  AND   FORCE 


45 


be  released  quickly.  Many  of  the  most  violent  explosives 
possess  less  stored-up  energy  than  the  same  weight  of 
other  materials,  but  in  the  case  of  the  explosive  the  energy 
is  all  released  in  an  instant,  while  with  a  substance  such 
as  coal  considerable  time  is  required  to  release  its  energy. 
When  powder  explodes,  a  gas  is  formed  which  would 
occupy  at  ordinary  pressure  several  hundred  times  as 


Eccentric 


FIG.  37.  —  Diagram  Showing  Action  of  Steam  in  a  Common  Steam  Engine  of 
the  Reciprocating  Type. 

much  space  as  the  original  powder.  In  the  gun  the  gas 
is  under  great  pressure  on  account  of  the  limited  space, 
and  as  it  expands  it  drives  the  bullet  or  projectile  rapidly 
before  it. 

Molecular  Forces.  —  In  the  case  of  gases,  the  mole- 
cules seem  to  have  little  attraction  for  each  other.  With 
liquids,  however,  the  molecules  resist  being  pulled  apart, 
and  with  solids  this  force  is  very  great,  as  is  shown  by 
the  weight  required  to  break  a  small  steel  wire. 

Elasticity.  -  -  The  tendency  of  a  substance  to  return  to 
its  original  form  and  volume  after  having  been  stretched 
or  distorted  is  called  elasticity.  Gases  have  perfect 
elasticity  of  volume,  but  they  have  no  shape.  The  elas- 


46 


GENERAL  SCIENCE 


ticity  of  air  is  the  property  which  makes  it  so  valuable 
as  a  shock  absorber  in  pneumatic  tires.  If  you  strike 
the  handle  of  a  bicycle  pump  when  the  outlet  is  closed, 
the  handle  will  fly  back  to  its  first  position. 

Almost   all   solids   are   elastic   to   some   extent.     You 
may   test   the   elasticity   of   rubber,    steel,   marble,  and 

wood  by  dropping 
balls  of  these  sub- 
stances on  a  slab 
of  iron  or  stone 
and  noting  the 
height  of  the  re- 
/  bound. 


FIG.   38.  —  A  Simple  Apparatus  for  Testing   the 
Elasticity  of  a  Wooden  Bar. 


Experiment  4.  — 

Test  the  bending 
elasticity  of  a  wooden  yardstick  (Figure  38)  by  adding  weights  to 
the  scale  pan  and  reading  the  amount  of  the  bend  from  the  scale. 
Is  there  any  relation  between  the  amount  of  the  bending  and  the 
weights  ?  Give  six  uses  of  elasticity  in  a  commercial  way. 

Cohesion  and  Adhesion.  -  -  The  attractive  force  which 
binds  molecules  of  the  same  kind  together  is  called  co- 
hesion, and  the  force  which  binds  together  molecules  of 
unlike  kind  is  called  adhesion.  It  is  cohesion  which 
produces  the  rigidity  of  solids,  and  it  is  adhesion  which 
enables  us  to  glue  together  two  pieces  of  wood.  This 
distinction  between  cohesion  and  adhesion  is  one  made 
simply  for  convenience  and  not  because  the  forces  are 
essentially  different.  We  have  no  reason  for  supposing 
that  the  force  holding  particles  of  wood  to  molecules  of 
glue  is  different  from  that  holding  molecules  of  glue 
together. 

If  a  piece  of  plate  glass  is  held  flat  on  the  surface  of 
water,  it  will  require  some  force  to  remove  it  (Figure  39) . 


ENERGY  AND   FORCE 


47 


FIG.  39.  — The  glass  plate  ad- 
heres to  the  water. 


If  we  examine  the  glass  after  it  has  been  removed,  we  shall 
find  it  wet,  showing  that  when  we  lifted  the  glass  plate, 
we  separated  water  molecules  from  water  molecules 
and  not  water  from  glass.  This 
force  may  be  measured  easily  by 
arranging  a  balance,  as  shown  in 
Figure  40,  and  determining  the 
weight  that  is  required  to  lift  the 
plate  of  glass  and  break  the  co- 
hesive force.  The  cohesive  force 
will  be  this  weight  less  the  actual 
weight  of  the  plate  of  glass.  If 
the  size  of  the  plate  is  known, 
the  force  per  square  inch  may 
be  easily  determined. 

Shape  of  Free  Liquid.  —  Small 
drops  of  a  liquid  are  spherical  in  shape,  for  the  surface 
of  a  sphere  is  the  minimum  surface  for  a  given  mass,  and 
the  cohesive  forces,  acting  between  the  molecules  of  a 

given  mass  of  liquid,  tend  to 
reduce  it  to  the  volume  hav- 
ing the  smallest  possible  sur- 
face. In  larger  quantities  of 
liquids,  the  force  of  gravita- 
tion is  large  enough  to  be 
more  of  a  factor  in  determin- 
ing the  shape  than  the  co- 
hesive forces,  hence  the  drops 
flatten  out. 

On  the  surface  of  a  liquid 
the  attractive  forces  between 


FIG.  40. —  Measuring  Cohesive  Force. 


the  molecules  are  sufficiently  strong  to  form  a  film.     A 
needle  which  is  much  heavier  than  water  may  be  floated 


48 


GENERAL  SCIENCE 


on  its  surface.     When  the  needle  breaks  through  the 
film,  it  sinks  quickly  to  the  bottom. 

Experiment  5.  - 
Make  a  wire  frame 
in  the  form  of  a  cube 
similar  to  the  one 
shown  in  Figure  41 
and  dip  it  into  a 
strong  solution  of 
soapsuds.  Note  the 
tendency  of  the  films 


FIG.  41.  —  Interesting  film  forms  may  be  obtained 
by  using  wire  frames  of  different  shapes. 


to  contract  to  the  shortest  lines  between  the  different  points  of  the 
cube. 

Experiment  6.  —  If,  after  blowing  a  soap  bubble,  one  discon- 
tinues before  the  bubble  breaks  from  the  tube,  the  bubble  will 
slowly  decrease  in  size  as  the  contraction  of  the  film  forces  the  air 
out. 

How  is  shot  made? 

Capillarity.  -  -  The  tendency  of  liquids  to  rise  in  hair- 
like  tubes  is  capillarity  or  capillary  attraction.  Capil- 
larity takes  place  in  all  fibrous  materials  as  well  as  in  tubes. 
The  rise  of  sap  in  trees  depends  largely  on  this  property. 

Experiment  7.  —  Heat  some  soft  glass  tubing  and  draw  it  out 
into  smaller  tubes.  Break  these  tubes  into  pieces  of  four  or  five 


FIG.  42.  — Capillarity. 
The  water  is  lifted  where  it  touches  glass,  while  the  mercury  is  depressed. 

inches  in  length.     Hold  them  vertically  and  lower  them  into  a 
glass  of  water.     Note  the  sudden  rise  of  the  water  in  the  tubes 


ENERGY  AND   FORCE 


49 


(Figure  42) .     In  which  tube  does  the  water  rise  the  highest  ?     Try 
mercury  instead  of  water.     What  happens  ? 

Touch  a  lump  of  sugar  to  the  surface  of  a  glass  of  water  and 
watch  the  rise  of  the  water.  Mention  other  examples  of  capil- 
larity. 

Capillary  action  is  due  to  two  forces,  cohesion  in  the 
water  or  liquid  and  adhesion  between  the  water  and  the 
tube.  If  a  glass  tube  of  large  diameter  is  used,  the  water 
is  raised  only  at  the  edges,  since  the  elastic  surface  of  the 
water  cannot  exert  enough  force  to  raise  all  the  water 
of  the  tube ;  but  if  the 
tube  is  small,  the  weight 
of  the  water  in  the  tube 
is  small  and  the  whole 
column  of  water  is  carried 
up  the  tube  by  the  force 
of  the  contraction  of  the 
elastic  surface.  We  no- 
ticed that  the  height  of 
the  water  was  different  in 

FIG.  43.  —  An  Example  of  Capillarity. 

tubes  of  different  diam- 

'  eter.  The  water  is  raised  in  each  case  until  its  weight  is 
just  equal  to  the  force  of  the  elastic  surface  of  the  water. 
Will  the  water  ever  run  out  of  the  top  of  the  tube  ?  Why  ? 

If  a  wick  is  wet  and  allowed  to  hang  over  the  side  of 
a  dish  of  water  (Figure  43),  the  water  will  rise  in  the  wick 
and  flow  over  the  side  of  the  dish.  The  flame  of  the 
kerosene  lamp  is  fed  by  the  oil  that  is  carried  to  it  by 
capillarity. 

Mention  three  uses  of  capillarity. 

Diffusion.  —  Diffusion  is  the  close  intermingling  of 
gases  or  liquids  which  takes  place  independently  of 
gravity  or  of  any  currents  in  the  substances  themselves. 


50  GENERAL  SCIENCE 

Experiment  8.  —  Introduce  a  solution  of  copper  sulphate 
into  the  bottom  of  a  hydrometer  jar  or  any  tall  jar  filled  with 
water.  This  may  be  done  by  pouring  the  solution  through  a  funnel 
tube  which  reaches  to  the  bottom  of  the  jar. 
Allow  the  jar  to  stand  for  a  few  days,  noting  the 
change  from  day  to  day  (Figure  44). 

Experiment  9.  —  Into    a   small   jar  put  a   few 
drops  of  strong  ammonia  water  and  cover  it  with 
a  piece  of  paper.     Into  a  second  jar  put  a  few  drops 
of   concentrated   hydrochloric   acid  and  invert  on 
the   first   jar.      Now    withdraw  the  paper.      The 
chemical  action  which  follows  is  evidence  of  the 
FIG  44  —The    raP^  diffusion  of  the  gases.     Although  these  gases 
copper  sulphata    are  not  visible,  their  presence  may  be  determined 

solution    slowly  by  thejr  odors.     As  they  diffuse,  a  new  substance 

diffuses  through  . 

the  entire  jar,  as  IS  formed. 

is  shown  by  the         Some  few  liquids  will  not  diffuse.    Devise  an  ex- 
change in  color.  periment  to  ghow  that  oil  and  water  will  not  diffuse. 

Can  you  put  oil,  alcohol,  and  water  into  the  same  bottle  so  that 
they  will  not  mix?     How? 

Osmosis.  —  Osmosis  is  the  diffusion  of  liquids  or  gases 
through  porous  walls  or  membranes. 

Experiment  10.  — Tie  a  piece  of  parchment  or  bladder  over  the 
mouth  of  a  large  funnel  tube,  and  after  having  filled  it  to  the 
depth  of  about  three  inches  with  a  saturated  solution  of  copper 
sulphate,  lower  the  funnel  end  into  a  jar  of  water  until  the  level 
of  the  solution  in  the  tube  is  the  same  as  that  of  the  water  in  the 
jar.  Support  it  in  this  manner  and  allow  it  to  stand  for  several 
hours,  when  it  will  be  found  that  the  blue  solution  is  several  inches 
higher  than  the  level  of  the  water  in  the  jar.  This  is  due  to  the 
fact  that  although  the  water  and  the  solution  pass  through  the 
membrane  in  opposite  directions,  the  water  passes  through  at  a 
much  more  rapid  rate,  thereby  diluting  and  increasing  the  volume 
of  the  solution  in  the  funnel  tube  (Figure  45).  The  water  in  the 
jar  gradually  acquires  a  blue  tinge,  proving  that  some  of  the  solu- 
tion of  copper  sulphate  has  passed  through  the  membrane  into  the 
jar.  If  the  water  and  the  solution  had  diffused  at  the  same  rate, 


ENERGY  AND   FORCE 


51 


there  would  have  been  no  change  in  the  level  of  the  liquids,  but 
osmosis  would  have  taken  place  just  the  same,  as  indicated  by  the 
color  of  the  liquids.  The  same  experi- 
ment may  be  performed  with  a  solution 
of  sugar  with  excellent  results.  By 
tasting  the  water  in  the  jar,  the  pres- 
ence of  sugar  may  be  detected. 

The  essential  for  an  experi- 
ment illustrating  osmosis  is  to 
have  two  solutions  of  different 
densities  separated  by  a  semiper- 
meable  partition.  Water  will 
pass  through  a  membrane  several 
times  as  fast  as  a  strong  salt  solu- 
tion, and  hydrogen  will  diffuse 
four  times  as  rapidly  as  air. 

Osmosis   is   important    in  the 
distribution  of  food  to  the  differ-          FIG.  45.— Osmosis, 
ent  parts  of  plants  and  animals.  Note  the  h^tt^ethe  liquid  in 
That  part  of  digestion  known  as 

absorption  is  largely  osmotic  action,  the  food  passing 
through  the  walls  of  the  stomach  and  the  intestines. 
Since  only  substances  known  as  crystalloids  pass  through 
animal  membranes,  starch,  which  is  an  amorphous  sub- 
stance and  a  very  important  article  of  food,  is  changed 
to  sugar  before  it  is  absorbed.  This  particular  kind  of 
osmosis  is  called  dialysis. 

Plants  get  most  of  their  nourishment  from  the'  soil, 
and  osmosis  seems  to  furnish  a  logical  explanation  of  the 
absorption  of  food  by  the  roots  of  plants.  By  the  pro- 
cess of  osmosis  the  roots  take  in  food  in  the  form  of  dilute 
solutions  which  contain  the  plant  food,  while  the  denser 
solution  of  cell  sap  inside  the  roots  does  not  pass  readily 


52  GENERAL  SCIENCE 

out  again.  Each  little  fiber  of  the  root  is  really  an  osmotic 
apparatus,  and  the  myriads  of  them  are  able  to  take 
in  sufficient  food  for  the  entire  plant.  Then,  assisted 
by  capillarity,  these  solutions  reach  the  different  parts 
of  the  plant  where  the  food  is  assimilated. 

QUESTIONS 

1.  Why  does  blotting  paper  absorb  ink  better  than  writing 
paper  ? 

2.  What  is  the  function  of  a  lamp  wick? 

3.  How  do  we  prove  that  air  is  matter? 

4.  What  property  of  matter  enables  us  to  blow  soap  bubbles? 

5.  What  are  the  laws  of  capillarity? 

6.  Why  do  feathers  fall  slowly  ? 

7.  What  force  causes  water  to  flow  in  streams  and  rivers  ? 

8.  If  the  earth  rotated  much  faster  than  it  does,  what  effect 
would  it  have  upon  the  weight  of  objects  at  the  equator?     At  the 
poles  ? 

9.  What  force  causes  a  postage  stamp  to  cling  to  an  envelope? 

10.  Why  does  thick  molasses  flow  more  slowly  than  water? 

11.  If  some  oil,  water,  and  mercury  were  placed  in  a  rotating 
vessel,    how   would   they   arrange   themselves    with   reference   to 
distance  from  the  center  of  the  vessel? 

.12.    How  does  air  affect  the  flight  of  a  thrown  ball? 

13.  Are  projectiles  and  rifle  balls  affected  by  the  wind?     How? 

14.  What  kind  of  energy  is  possessed  by  the  water  behind  a 
dam? 

15.  What  makes  a  pendulum  move  back  and  forth?     Why 
does  a  short  pendulum  move  faster  than  a  longer  one  ? 

16.  What  is  the  reason  an  automobile  skids?     Why  are  chains 
used  on  automobile  wheels  ? 

17.  Which  is  greater,  the  cohesive  force  between  water  par- 
ticles or  the  adhesive  force  between  water  and  glass  ?     How  may 
you  determine  the  truth  of  your  answer? 

18.  Why  is  a  golf  ball  so  elastic?      *  . 


CHAPTER  IV 

MACHINES 

THE  adage  "  Necessity  is  the  Mother  of  Invention  " 
is  especially  applicable  in  respect  to  the  uses  to  which 
man  has  put  machines.  Work  is  often  accomplished 
more  easily  by  the  use  of  some  simple  machine  than  in 
any  other  way.  Sometimes  it  is  quite  impossible  to 
accomplish  a  certain  piece  of  work  without  the  aid  of  a 
machine.  For  example,  the  man  who  desires  to  lift  a 
weight  of  1000  pounds  finds  that  it  is  beyond  his  power. 
With  the  aid  of  a  lever  the  task  is  easily  performed. 
And  so  it  is  with  a  multitude  of  applications  of  the  me- 
chanical principles.  If  materials  are  to  be  raised  to  the 
top  of  a  building,  a  rope  and  pulley  are  used.  If  heavy 
logs  are  to  be  loaded  on  trucks,  the  inclined  plane  is 
used.  If  a  building  is  to  be  lifted  from  its  foundations, 
the  screw  is  used. 

The  Evolution  of  Machines.  —  Machines  have  been 
the  greatest  of  civilizing  agencies.  Primitive  man  knew 
nothing  concerning  even  the  simplest  machines.  He 
did  not  realize  that  he  had  any  use  for  such  devices. 
'The  sling  was  probably  the  first  mechanical  device  used 
by  man.  With  it  he  could  throw  a  stone  with  sufficient 
force  to  make  it  a  valuable  weapon  for  protection  and 
for  securing  food.  Since  that  time  all  ages  have  had 
their  inventors.  The  sling  was  followed  by  the  lever 
and  the  sharp  bone  or  sharp  stone,  used  as  a  cutting 

53 


54  GENERAL  SCIENCE 

instrument.  These  simple  devices  enabled  man  to  live 
better  and  started  him  on  the  road  to  civilization.  His 
thinking  resulted  in  better  places  to  live,  in  better  pro- 
tection from  his  enemies,  and  in  better  food.  He  learned 
that  useful  plants  would  thrive  better  if  they  were  cared 
for,  and  thus  began  the  simplest  forms  of  agriculture. 
From  this  time  on  the  development  has  been  very  rapid. 
Man  has  learned  to  harness  the  various  forces  of  nature 
and  set  them  to  work  doing  the  countless  tasks  that 
his  fancy  and  needs  have  set  for  them.  Each  genera- 
tion has  had  the  enormous  advantage  of  the  cumulative 
results  of  the  thinking  of  all  previous  generations  in  the 
extent  of  its  inventions.  At  present  our  daily  life  is  so 
intimately  related  to  the  mechanical  world  through 
its  devices  for  producing,  collecting,  and  distributing 
food,  for  transportation,  and  for  communication,  that  the 
very  existence  of  many  people  depends  upon  it. 

The  six  simple  machines  are :  the  lever,  pulley,  wheel 
and  axle,  inclined  plane,  wedge,  and  screw.  It  is  some- 
times difficult  to  believe  that  the  modern  machines  use 
no  more  than  these  six  mechanical  principles  in  the  com- 
plicated motions  they  make  and  in  doing  the  wonder- 
ful things  they  do,  but  a  careful  analysis  will  show  that 
these  machines  are  made  up  entirely  of  combinations 
of  the  six  simple  machines. 

The  Principle  of  Work.  —  A  machine  cannot  create 
any  energy  nor  can  it  do  work  unless  work  is  done  upon 
it.  A  machine  is  simply  an  apparatus  which  enables 
us  to  apply  force  advantageously. 

When  a  force  moves  a  body  on  which  it  acts,  we  say 
that  work  has  been  done  upon  that  body.  The  amount 
of  work  done  is  always  equal  to  the  force  multiplied  by 
the  distance  through  which  it  moves  the  body.  Thus 


MACHINES 


55 


if  a  one-pound  weight  is  lifted  two  feet,  we  say  that  the 
work  done  is  equal  to  two  foot  pounds. 

Experiment  1 1 .  —  Pass  a  cord  over  a  pulley  as  shown  in  Figure 
46.  Attach  a  spring  balance  F  to  the  end  of  the  cord  and  a  weight 
W  to  the  other  end.  What  force  is  required  to 
support  the  weight  ?  Weigh  the  weight  W.  The 
force  and  weight  in  this  case  will  be  found  to  be 
the  same.  If  F  moves  a  certain  distance,  W  will 
be  moved  up  an  equal  distance.  The  force  multi- 
plied by  the  distance  through  which  it  moves  will 
just  equal  the  weight  multiplied  by  the  distance 
through  which  it  moves.  If  d  is  the  distance  F 
moves  and  d'  the  distance  W  moves,  then 

Fd  =  Wd' 


This  is  the  general  law  of  all  machines. 
The  power  or  force  multiplied  by  the  dis- 
tance through  which  it  acts  equals  the 
resistance  or  weight  multiplied  by  the 
distance  through  which  it  acts. 


FIG.  46.  —  The 
advantage  of  a  fixed 
pulley  is  simply  one 
of  direction. 


The  Lever.  —  This  is  the  most  common  of  all  the  sim- 
ple machines.  It  is  a  bar  of  any  kind  arranged  to  turn 
on  a  rest  or  pivot,  called  its  fulcrum.  The  power  is  the 


FIG.  47. 


force  applied  to  any  part  of  the  lever  and  the  weight  is 
the  body  to  be  moved  or  balanced  by  the  application 
of  power. 


56  GENERAL  SCIENCE 

Experiment  12. —  Pierce  a  meter  stick  in  the  center  and  balance  it 
on  a  nail  as  shown  in  Figure  47.  By  means  of  a  thread  suspend  a 
200-g.  weight  at  A,  20  cm.  from  the  point  of  support,  the  fulcrum. 
Hang  a  100-g.  weight  on  the  other  arm  of  the  lever  and  move  it  until 
the  bar  just  balances.  It  will  be  found  that  the  100-g.  weight  is  40  cm. 
from  the  fulcrum. 

Wxd    =     Fxd' 
200x20  =  100x40 

Perform  the  experiment  with  other  weights  at  different  distances 
from  the  fulcrum.  Does  the  law  hold  in  every  case  ? 

Classes  of  Levers.  —  There  are  three  classes  of  levers 
depending  upon  the  relative  location  of  the 'power,  the 
fulcrum,  and  the  weight.  In  the  lever  of  the  first  class 
(Figure  48),  the  fulcrum  is  placed  between  the  weight  and 


FIG.  48.  —  Lever  of  the  First  Class. 

the  power.     Scissors,  weighing  balances,  pump  handles, 
and  crowbars  are  examples  of  this  class  of  lever. 

In  the  lever  of  the  second  class  (Figure  49)  the  weight 
is  between  the  fulcrum  and  the  power.     The  nutcracker 

IP  ' 


FIG.  49.  —  Lever  of  the  Second  Class. 


and  the  wheelbarrow  are  levers  of  the  second  class.  In 
the  nutcracker  the  hinge  is  the  fulcrum,  the  nut  is  the 
weight,  and  the  force  applied  to  the  handles  is  the  power. 


MACHINES  57 

In  the  lever  of  the  third  class  (Figure  50),  the  power 
is  between  the  fulcrum  and  the  weight,  as  in  sugar  tongs, 
sheep  shears,  and  the  treadle  on  a  sewing  machine. 


FIG.  50.  —  Lever  of  the  Third  Class. 


EXERCISES 

1.  What  kind  of  lever  is  a  claw  hammer  when  used  to  pull  a 
nail?     The  oar  of  a  boat?     Wire  cutters? 

2.  A  man  places  a  fulcrum  1  foot  from  the  end  of   a  6-foot 
crowbar.     If  he  presses  down  on  the  other  end  with  a  force  equal 
to  150  pounds,  what  weight  can  he  raise? 

3.  With  the  same  power  and  bar,  what  weight  can  he  raise  if 
the  fulcrum  is  placed  6  inches  from  the  end  ? 

4.  On  a  balanced  meter  bar  a  weight  of  300  g.  is  placed  30 
cm.  from  the  point  of  support.     Where  must  a  weight  of  450  g. 
be  placed  to  balance  it  ? 

5.  Where  is  the  fulcrum  in  a  wheelbarrow?     The  weight? 
The  power? 

6.  What  kind  of  lever  is  the  forearm?     Why  is  it  better  than 
another  class  of  lever? 

7.  What  advantage  is  gained  in  a  lever  when  the  power  is 
quite  close  to  the  fulcrum,  as  in  the  case  of  a  boat  oar  ? 

8.  Name    three    uses    of    the    lever    not  mentioned   in    this 
book? 

9.  A  200-pound  weight  is  placed  1  foot  from  the  axle   of  a 
wheelbarrow.      How  much  force  must  be  exerted  on  the  handles 
5  feet  from  the   axle  to  lift  the  weight  ?     (The  weight  of  the 
wheelbarrow  is  not  considered  in  this  problem.) 

10.  An  oar  is  1\  feet  long  and  the  oarlock  is  1^  feet  from  the 
handle.  If  a  man  pulls  on  the  oar  with  a  force  of  100  pounds, 
what  force  is  exerted  on  the  water? 


58 


GENERAL  SCIENCE 


Pulleys.  —  Figure  51   represents  the  use  of  a  single 
fixed  pulley.     In  this  pulley  the  only  advantage  gained 

a is  direction.     By  pulling  down  we  may 

lift  a  body  vertically,  but  we  cannot 
lift  more  than  the  equivalent  of  the 
force  applied  at  F. 

Arrange  the  pulley  and  spring  bal- 
ance as  shown  in  Figure  52,  so  that  a 
single  movable  pulley  is  attached  to  the 
weight  W.  It  is  quite  evident  that 
the  weight  is  supported  equally  by 
each  strand  of  the  rope. 
This  may  be  verified  * 
by  the  spring  balance. 
FIG.  51.— single  Fixed  it  should  be  understood, 

Pulley. 

however,  that  the  weight 
at  W  includes  the  weight  of  the  pulley. 

Make  a  test  to  see  how  far  the  force 
must  be  moved  to  move  the  weight  a 
distance  of  1  foot.  Does  the  law  of 
machines  hold  in  this  case  of  the  pulley? 

Other  arrangements  of  pulleys  are 
shown  in  Figure  53.  In  each  case  there 
are  four  strands  of  rope  supporting  the 
weight.  Then  the  force  necessary  to 
support  W  is  one  fourth  of  the  total 
weight,  or  the  weight  equals  the  force  FIG.  52.— Measur- 
multiplied  by  the  number  of  supporting  ft^USSS 

Strands  Of  rope.  Movable  Pulley. 

W  -  Fn 

With  most  arrangements  of  pulleys  there  is  so  much 
friction  that  it  may  seem  that  the  law  does  not  hold. 


MACHINES 


59 


The  best  way  to  measure  the  force  is  to  take  the  mean 
of  the  force  which  will  just  cause  the  weight  to  ascend 


A.  B.   Block  and  tackle. 

FIG.  53.  —  A  Common  Way  of  Arranging  Pulleys  for  Lifting  Heavy  Weights. 

slowly  and  that  which  will  just  cause  it  to  move  down 
slowly. 

EXERCISES 

1.  Draw  a  diagram  of  pulleys  arranged  so  that  50  pounds  will 
support  100  pounds. 

2.  Hay  is  sometimes  carried  from  the  wagon  to  the  mow.     Can 
you  arrange  a  set  of  four  pulleys  to  do  this? 

Wheel  and  Axle.  —  Figure  54  shows  a  diagram  of  a 
simple  form  of  the  wheel  and  axle.  If  the  radius  OA  of 
the  wheel  is  four  times  the  radius  OC  of  the  axle,  then 
one  pound  of  force  will  support  four  pounds  of  weight 
on  the  axle.  Of  course  if  the  radius  of  the  wheel  is  four 


60 


GENERAL  SCIENCE 


times  the  circumference  of  the 
axle,  the  force  F  will  move  four 
times  as  far  as  the  weight  W,  or 

Weight  X  distance  through  which  it 
moves 

=  Force  X  distance  through 
which  it  moves. 

In  the  windlass,  which  is  a 
common  form  of  the  wheel  and 
axle,  a  crank  takes  the  place  of 
the  wheel  (Figure  55).  The 
principle,  however,  is  exactly  the 
same.  Figure  56  shows  how 
two  machines  of  the  wheel-and-axle  type  may  be  com- 
bined to  lift  enormous  weights. 

EXERCISES 

1.  Name  three  uses  of  the  wheel  and  axle. 

2.  The  radius  of  a  wheel  is  2  feet  and  that  of  the  axle  4  inches. 
What  force  will  be  required  to  overcome  a  weight  of  600  pounds? 


FIG.  54.  —  Wheel  and  Axle. 


FIG.  55.  —  Tiie  Windlass. 

3.  What  kind  of  machine  is  a  capstan?     A  coffee  grinder?     A 
bicycle  pedal? 


MACHINES 


61 


4.  If  a  bicycle  pedal  is  7  inches  long  and  the  radius  of  the 
sprocket  wheel  is  3^  inches,  what  pull  will  be  exerted  on  the  sprocket 
wheel  by  a  force  of  50  pounds  on  the  pedal  ? 

The  Inclined  Plane.  —  Arrange  a  board  as  shown  in 
Figure  57,  so  that  it  makes  an  angle  of  20  or  30  degrees 

with  the  table.  In  the  absence 
of  a  carriage,  a  roller  skate  may 
be  used.  Find  the  mean  of  the 
force  at  F  that  will  just  cause 
the  carriage  to  move  up  the  in- 
cline slowly,  and  that  will  just 
cause  it  to  move  down  the  in- 
cline slowly.  Then 

F  X  length  of  incline  (I) 
=  W  X  height  of  plane  (h) 

FIG.  56. -A  Combination  of  Tne  inclined  plane  is  used  in 
wheels  and  Axles  to  Lift  Heavy  loading  all  sorts  of  heavy  mate- 

Weights-  -i  j  j.      i        An- 

nals on  cars  and  trucks.     When 

the  objects  to  be  loaded  are  round,  such  as  barrels,  they 
are  simply  rolled  on  the  plane.     Such  objects  as  pianos 


FIG.  57.  —  Inclined  Plane  and  Truck. 


62 


GENERAL  SCIENCE 


are   put  on  low-wheeled  carriages   and   moved   up   the 

plane. 

The  Screw.  —  Cut  a  piece  of  paper  in  the  form  of  a 

right-angled  triangle  (Figure  58) ;  the  side  C  is  an  in- 
clined plane.  Wind  the  paper 
around  a  pencil,  and  it  has  the 
appearance  of  a  screw.  Can  you 
follow  the  inclined  plane  from 
the  bottom  to  the  top  of  the 
pencil?  The  elevation  made  in 
one  turn  is  called  a  thread. 

A  stairway  is  a  common  form 
of  inclined  plane.  Stairways  are 
often  arranged  in  towers  and 
lighthouses  in  the  form  of  a 


FIG.  58.  —  Showing  the  Principle 
Involved  in  the  Screw. 


spiral,  the  inclined  plane  turning  round  and  round  the 
inside  of  the  tower.  The  reason  the  screw  is  so  powerful 
is  that  the  power  moves  through  such  a  long  distance 
while  the  screw  moves  a  very  small  distance.  In  the 
jackscrew  in  Figure  59,  suppose 
the  handle  to  be  4  feet  long  and 
the  pitch  of  the  screw  one  half 
an  inch.  Then  as  the  end  of  the 
handle  moves  around  the  circle 
25  feet  (4  X  2  X  3.1416)  in  cir- 
cumference, the  screw  is  moved 
up  one  half  an  inch.  A  force 
of  one  pound  exerted  at  the  end  FlG-  59— Liftin€  Jack' 
of  the  handle  will  lift  600  pounds  at  W,  since  one  half  an 
inch  is  contained  600  times  in  25  feet. 

The  wedge  is  a  machine  used  for  splitting  and  forcing 
materials  apart  where  great  power  is  required.  Figure 
60  illustrates  the  use  of  a  wedge.  If  the  wedge  is  12  inches 


MACHINES 


63 


FIG.  60.  —  The  Wedge. 


long  and  2  inches  thick  at  the  thickest  part,  how  far  will 
the  force  have  moved  when  the  wedge  has  been  driven 
into  the  block?     How  does  the 
amount  of  work  done  compare 
with  the  force  applied  ? 

The  wedge  may  be  considered 
as  an  inclined  plane  which  is 
forced  by  blows  between  two 
resistances  in  such  a  way  as  to 
separate  them. 

Mechanical  Advantage.  —  It 
is  often  possible  with  the  aid  of 
a  machine  to  overcome  a  certain 
resisting  force  by  applying  a 
much  smaller  force.  The  ratio  of  the  resistance  overcome 
to  the  force  applied  is  called  the  mechanical  advantage 
of  the  machine.  Thus  if  both  arms  of  a  lever  of  the 
first  class  are  of  the  same  length,  the  mechanical  advan- 
tage will  be  1.  If  the  force  arm  is  two  times  as  long  as 
the  resistance  arm  the  mechanical  advantage  will  be  2, 
while  if  the  force  arm  is  one  half  as  long  as  the  resistance 
arm,  the  mechanical  advantage  will  be  one  half. 

Suppose  the  force  arm  of  a  lever  of  the  first  class  to  be 
four  feet  long  and  the  resistance  arm  to  be  one  foot  long, 
then  a  force  of  one  pound  will  overcome  a  resistance  of  four 
pounds  ;  but  it  will  be  noticed  that  the  acting  force  moves 
four  times  as  far  as  the  resisting  force  and  also  four  times 
as  fast.  We  can  sacrifice  speed  and  distance  to  gain  force 
or  we  can  sacrifice  force  to  gain  speed  or  distance. 

Efficiency  in  Machines.  —  Not  all  the  force  applied 
to  a  machine  is  effective  in  doing  useful  work.  Some 
work  must  be  done  in  overcoming  friction  in  the  machine 
and  in  moving  parts  of  the  machine  itself. 


64 


GENERAL  SCIENCE 


If  three  fourths  of  the  force  applied  to  a  machine  is 
available  for  useful  work,  while  one  fourth  is  used  in 
overcoming  friction  in  the  machine  and  moving  its  parts, 
we  say  the  efficiency  of  the  machine  is  75  per  cent. 

Many  ways  have  been  devised  for  reducing  friction 
and  thus  increasing  the  efficiency  of  machines.  Roller 


FIG.  61.  —  A,  Common  Bearing;  B,  Ball  Bearing;  C,  Roller  Bearing. 

and  ball  bearings  greatly  reduce  friction  by  substituting 
rolling  friction  for  sliding  friction  (Figure  61). 

Experiment  13.  —  Determine  the  force  necessary  to  slide  a  mass 
of  500  grams  over  a  level  table  top.  Now  determine  the  force 
necessary  to  move  a  similar  mass  on  wheels.  Which  is  greater, 
the  sliding  friction  or  the  rolling  friction?  What  effect  has  lubri- 
cating oil  on  sliding  friction  ? 

EXERCISES 

1.  What  power  must  be  exerted  to  roll  a  barrel  weighing  300 
pounds  up  a  plank  10  feet  long  into  a  wagon  3  feet  high? 

2.  Mention  three  uses  of  the  inclined  plane. 

3.  The  diameter  of  the  wheel  on  a  letter  press  is  16  inches. 
The  pitch  of  the  screw  is  one  half  inch.     What,  pressure  will  be 
produced  by  a  force  of  100  pounds  applied  to  the  wheel? 

4.  How  may  the  pitch  of  a  screw  be  determined? 

5.  Why  is  it  difficult  to  walk  on  highly  polished  floors? 

6.  Has  friction  any  value? 

7.  Mention  four  uses  of  rollers  to  reduce  friction. 

8.  What  causes  bearings  to  become  hot? 

9.  How  long  must  an  inclined  plane  be  so  that  a  force  of  100 
pounds  will  roll  a  barrel  weighing  400  pounds  into  a  wagon  3  feet 
high? 


MACHINES  65 

10.  The  nuts  on  one  side  of  a  wagon  have  right-handed  threads 
and  on  the  other  side  left-handed  threads.     Why? 

11.  State  the  general  law  of  machines. 

12.  What  is  the  advantage  of  using  iron  rails  on  a  railroad? 

13.  Why  do  wide- tired  wagon  wheels  make  hauling  over  soft 
fields  easier? 

14.  Why  do  we  scatter  sawdust  on  icy  pavements? 

Power.  -  -  The  term  power  is  one  which  is  used  quite 
generally  to  designate  sources  of  energy,  but  power  in  a 
specific  sense  means  the  rate  of  doing  work.  Time  is 
not  a  factor  in  the  determination  of  work.  The  same 
amount  of  work  will  be  done  in  moving  a  ton  of  coal 
into  the  basement  whether  the  work  be  done  in  two  hours 
or  ten  hours,  but  the  rate  at  which  energy  is  consumed 
will  be  much  greater  when  the  work  is  done  in  two  hours. 
An  engine  which  can  do  a  certain  piece  of  work  in  an 
hour  has  twice  as  much  power  as  one  which  can  do  but 
half  the  work  in  an  hour.  The  first  engine  liberates 
energy  faster  than  the  second. 

Unit  of  Power. — The  unit  of  work  in  the  English  system 
is  the  foot  pound,  the  unit  of  time  is  the  second,  and  the 
unit  of  power  is  a  foot  pound  of  work  in  a  second,  or 

Work  p     W 

Power  =  TH; —  written  P  =  •=r 
Iime  1 

If  W  and  T  are  unity,  then  P  equals  one  foot  pound 
per  second. 

It  is  quite  common  now  to  speak  of  the  rating  of  an 
engine  or  motor  in  terms  of  horse  power.  Cf.  page  44. 

Man  has  learned  to  use  the  energy  that  is  stored  in 
nature  to  aid  him  in  the  operation  of  his  machines. 
The  energy  of  the  wind,  the  water,  the  sun,  and  that 
stored  in  materials  used  as  fuels  and  foods  is  utilized  in 
this  way. 


66 


GENERAL  SCIENCE 


Water  Power.  -  -  The  power  of  water  is  very  great. 
As  we  watch  the  water  in  a  small  stream  trickling  over 
the  pebbles,  we  can  hardly  appreciate  the  vast  power 
that  results  when  the  stream  is  dammed  and  a  consider- 
able head  of  water  maintained.  The  force  of  the  waves 


f  FIG.  62. —  Flour  Mills  on  the  Mississippi  River. 

and  of  flood  waters  often  does  immense  damage  to  ship- 
ping, to  crops,  and  to  the  works  of  man  which  have  been 
built  in  their  paths. 

It  is  much  more  difficult  to  row  a  boat  or  to  swim  against 
the  current  of  a  stream  than  with  it,  since  water  exerts 


MACHINES 


'67 


a  force  in  the  direction  in  which  it  is  flowing.     The  power 

of  many  streams  can  be  used  in  factories,  in  mills,  and 

for  making  electricity,  which  can 

be  utilized  in  numerous  ways. 
Some   of    the   power   of    the 

Niagara  River  is  used  to  turn 

great  dynamos,   which    develop 

the  electricity  used  in  the  near-by 

cities  of  the  United  States  and 

Canada.      The   mills   of    many 

New  England  cities  are  run  by 

water  power.     The  largest  flour 

mills  in  the  world   are  run  by 

the    water    of    the    Mississippi 

River  (Fig.  62). 

Several  types  of  water  wheels 

are  used  to  transform  the  poten- 
tial energy  of  the  water  above  into  mechanical  energy. 
The  Overshot  Wheel.— This  type  of  wheel  (Figure  63) 

utilizes  the  weight  of 
the  water  at  A.  The 
work  expended  on  the 
wheel  in  a  second  is 
the  product  of  the 
weight  of"  the  water 
which  falls  upon  it  in 
a  second  and  the  dis- 
tance through  which 
it  falls.  This  is  a 
very  efficient  type  of 
water  wheel  and  is 

the  common  type  in  hilly  regions  where  the  streams  are 

small  and  have  considerable  fall. 


FIG.  63.  —  Overshot  Water 
Wheel. 


FIG.  64.  —  Undershot  Water  Wheel. 


68 


GENERAL  SCIENCE 


The  Undershot  Wheel.  —  This  type  of  wheel  (Figure 
64)  is  much  less  efficient  than  the  overshot  wheel  and  is 
used  in  more  level  regions  where  there  is  an  abundance 
of  water  and  little  fall.  It  utilizes  the  kinetic  energy 
of  the  water  as  it  runs  through  the  opening  0.  Such  a 
wheel  seldom  develops  more  than  25  per  cent  of  the  po- 
tential energy  of  the  water  above  the  dam. 

The  Water  Turbine.  —  This  form  of  water  wheel  is  now 
used  more  than  any  other.  Figure  65  shows  the  instal- 
lation of  such  a  wheel. 
It  rotates  in  a  horizontal 
plane  and  stands  at  the 
bottom  of  a  turbine  pit. 
The  power  developed  de- 
pends upon  the  depth  of 
the  pit  and  the  amount 
of  water  which  passes 
through  the  wheel.  The 
efficiency  of  the  turbine 
is  often  as  high  as  90  per 
cent.  It  is  used  exclu- 
sively in  the  power  plants 
at  Niagara,  where  the 
pits  are  about  135  feet 
deep  and  where  indi- 
vidual turbines  develop 
as  high  as  5000  horse 
power. 

Wind  Power.  —  Wind  power  like  water  power  is  to 
be  commended  for  its  cheapness.  The  principle  of  the 
windmill  is  exactly  the  same  as  that  of  the  water  wheel. 
Moving  air  strikes  the  blades  of  the  windmill  and  causes 
the  wheel  to  rotate  (Figure  66) .  This  mechanical  energy 


FIG.  65.  —  Diagram  of  Water  Turbine. 


MACHINES 


69 


is  used  to  pump  water,  grind  corn,  and  do  other,  kinds 
of  work  which  the  farmer  has  to  do.  In  Holland  the 
water  is  pumped  from  the  lowlands  (Figure  67)  by  numerous 
windmills.  The  sailboat  is  a  contrivance  for  utilizing 
the  power  of  the  wind  for  travel  and  transportation  on 

water.   The  sail  of    ^___ 

the  boat  merely 
provides  a  large 
area  of  resistance 
to  the  wind. 

The  Aeroplane. 
—  There  are  a 
number  of  craft 
to  which  the  term 
airship  may  prop- 
erly be  applied, 
but  the  aeroplanes 
only  are  properly 
called  flying  ma- 
chines. They  are 
maintained  in 
their  positions  by 
the  resistance  of 
the  air.  When 
the  motor  is  work- 
ing, the  aeroplane 
is  driven  rapidly 
forward  by  the  action  of  the  propeller  against  the  resist- 
ing air.  Then  when  the  plane  or  planes  of  the  airship  are 
tilted  upward,  the  resistance  which  the  air  offers  to  their 
forward  movement  causes  the  machine  to  move  upward. 
The  aeroplane  is  heavier  than  air  and  must  be  in  rapid 
forward  motion  in  order  to  maintain  its  position  in  the  air. 


FIG.  66.  —  Windmill. 


70 


GENERAL  SCIENCE 


The  Steam  Engine.  —  When  water  changes  to  steam, 
its  volume  increases  about  1600  times.  That  is,  one 
liter  of  water  will  make  1600  liters  of  steam  at  standard 
pressure.  Steam  is  a  gas,  and  the  molecules  of  all  gases 
move  about  rapidly.  The  higher  the  temperature  the 

more  rapidly  they 
move  and  the 
harder  they  strike 
the  walls  of  any 
containing  ves- 
sel. Since  this  is 
true,  the  mole- 
cules of  com- 
pressed steam,  as 
of  any  other  com- 
pressed gas,  will 
rush  rapidly 
through  any  pas- 
sage that  is  of- 
fered for  them 
from  a  chamber 
which  incloses 
them.  This 
stream  of  gas  has 
the  power  of  doing 
work.  Figure  37 
shows  the  essen- 
tial parts  of  a  double-acting  steam  engine.  The  steam 
is  produced  under  high  pressure  in  the  boiler  and  is 
allowed  to  expand  in  the  cylinder,  first  on  one  side 
of  the  piston  and  then  on  the  other,  thus  forcing  the 
piston  rapidly  to  and  fro.  This  motion  is  converted  into 
the  type  of*  motion  desired,  by  a  shaft  and  cogwheels 


FIG.  67.  —  A  Windmill  in  Holland. 


MACHINES 


71 


and  pulleys.     The  eccentric  controls  the  exhaust  of  the 
used  steam. 

The  Steam  Turbine.  —  This  is  a  form  of  the  steam 
engine  which  converts  the  energy  of  steam  into  mechanical 
energy  in  much  the  same  way 
that  the  water  turbine  converts 
the  energy  of  falling  water  into 
mechanical  energy  (Figure  68). 
Steam  is  directed  by  nozzles 
against  the  blades  of  the  turbine 
wheel,  which  is  caused  to  revolve 
at  a  very  high  rate  of  speed .  The 
steam  can  be  used  several  times 
by  arranging  the  turbines  in 
series.  Such  engines  are  used  on 
the  great  ocean  liners  and  where  FlG-  68-  —  The  Principle  of  the 

,  -11  Steam  Turbine. 

tremendous  power  is  needed. 

Gasoline  Engines. --The  force  in  the  gasoline  engine 
is  that  of  expanding  gases  formed  by  the  explosion  of 
gasoline  vapor  and  air. 


A  Gasoline  Engine. 


72  GENERAL  SCIENCE 

QUESTIONS 

1.  What  important  inventions  did  James  Watt  make? 

2.  How  many  foot  pounds  a  minute  is  a  horse  power? 

3.  Name  one  disastrous  flood  and  tell  something  of  the  extent 
of  the  damage. 

4.  Where  are  the  largest  flour  mills  in  the  world? 

5.  Explain  how  we  may  travel  in  a  sailboat  in  other  directions 
than  with  the  wind. 

6.  Why  do  windmills  not  work  at  all  times  when  the  wind  is 
blowing? 

7.  Of  what  use  is  a  keel  on  a  boat? 

8.  What  influence  did  the  development  of  the  gas  engine  have 
upon  the  invention  of  the  aeroplane? 

9.  What  is  a  stationary  engine? 

10.  Name  six  uses  of  the  steam  engine. 

11.  What  is  the  principal  use  of  the  gas  engine? 

12.  From  where  does  the  energy  of  the  steam  and  gas  engines 
really  come? 

13.  What  mechanical  principles  are  involved  in  the  construc- 
tion of  the  ordinary  farm  wagon  ? 

14.  Name  six  uses  of  the  pulley. 

15.  What  force  is  utilized  by  the  wheel  brake  on  a  wagon? 
On  an  automobile  ?     On  a  railway  car  ?     How  is  this  force  applied 
in  each  case? 


CHAPTER  V 
THE   ATMOSPHERE 

THE  atmosphere  is  a  light,  transparent  mixture  of 
gases.  It  rests  upon  the  land  and  the  sea,  forming  the 
outermost  part  of  the  earth.  The  atmosphere  becomes 
less  dense  as  the  distance  from  the  earth's  crust  increases, 
one  half  of  it  being  within  four  miles  of  the  solid  earth. 
The  change  in  density,  however,  is  very  gradual.  Just 
how  deep  the  atmosphere  is  we  cannot  tell,  but  there  is 
probably  very  little  of  it  beyond  a  distance  of  fifty  miles 
from  the  crust  of  the  earth,  although  it  has  been  estimated 
that  there  is  some  atmosphere  at  a  distance  of  two  hun- 
dred miles. 

The  principal  gases  of  the  atmosphere  are  nitrogen 
and  oxygen  mixed  with  a  small  amount  of  argon  and 
carbon  dioxide.  Below  is  a  table  showing  the  approxi- 
mate percentage  of  each  gas  in  the  atmosphere,  although 
the  amounts  vary  slightly. 

Nitrogen 78  per  cent 

Oxygen.     .     .     .    „     .     ...,-.      21  per  cent 

Argon .     .  v    V       1  per  cent 

Carbon  dioxide 03  per  cent 

A  number  of  experiments  may  be  devised  to  prove  that 
air  is  matter.  We  cannot  see  air,  but  we  are  concerned 
with  it  every  moment  of  our  lives,  and  we  have  only  to 
stand  out  of  doors  on  a  windy  day  to  be  convinced  of  its 
reality. 

73 


74 


GENERAL  SCIENCE 


Experiment  14.  —  Fit  a  bottle  with  a  one-hole  rubber  stopper 
and  attempt  to  pour  water  into  it  through  a  thistle  tube  (Figure 

69).     What  property  of  matter  is 
demonstrated  by  this  experiment? 
Experiment  15.  —  Place  a  cork 
with  a  small  piece  of  lighted  candle 
on  it  in  a  jar  of  water.     Invert  a 
small  jar  over  the  cork  and  force 
.  it  down  into  the  water  in  the  jar. 


FIG.  69.  —  Impenetrability  is  one  of 
the  general  properties  of  matter. 


FIG.  70. 


The  candle  may  be  seen  burning  below  the  level  of  the  water  in 
the  first  jar  (Figure  70). 

Weight  of  the  Atmosphere.  —  The  atmosphere  is  drawn 
toward  the  center  of  the  earth  as  all  other  substances  are, 
and  since  weight  is  the  measure  of  this  force,  air  has 
weight.  - 

Experiment  16.  —  Exhaust  the  air  from  the  hollow  globe  of  a 
Florence  flask  and  weigh  the  flask  carefully  on  a  suitable  balance. 
Then  admit  air  to  the  flask  and  weigh  again  (Figure  71).  What  is 
the  result?  A  cubic  foot  of  air  weighs  a  little  more  than  one  and 
one  quarter  ounces. 

Air  Pressure.  —  Since  air  has  weight,  it  must  exert 
pressure  upon  all  bodies  immersed  in  it.  If  a  small 
hand  glass  is  placed  on  the  receiver  of  an  air  pump  and 


THE  ATMOSPHERE 


75 


some  of  the  air  exhausted  after  placing  one  hand  over 
the  glass,  some  idea  may  be  gained  of  the  extent  of  this 
pressure.  The  experiment  may  be  performed  in  a  slightly 


FIG.  71.  —  Weighing  Air. 


FIG.  72.  —  The  pressure  of  the  air 
forces  the  rubber  diaphragm  into 
the  bell-jar. 


different  way  by  tying  a  piece  of  sheet  rubber  over  the 
hand  glass  and  then  exhausting  the  air  (Figure  72). 

The  pressure  of  the  atmosphere  is 
usually  measured  by  the  barometer,  the 
most  accurate  kind  being  the  mercurial 
barometer  (Figure  73),  which  consists  of 
a  strong  glass  tube  about  thirty-one 
inches  long  and  closed  at  one  end.  The 
tube  is  filled  with  mercury  and  inverted 
in  a  cup  of  mercury.  At  or  near  the  sea 
level  the  mercury  in  the  tube  will  stand 
at  a  height  of  about  twenty-nine  or 
thirty  inches,  leaving  a  vacuum  at  the 
top  of  the  tube.  Since  this  column  of  FIG.  73.— This  type 
mercury  is  held  up  by  the  pressure  of  £ 
the  atmosphere  on  the  mercury  in  the  made. 


76 


GENERAL  SCIENCE 


30  lit 


cup,  it  must  weigh  the  same  as  a  column  of  air  of  equal 
cross  section  and  extending  as  high  as  there  is  any  at- 
mosphere (Figure  74). 

Torricelli  first  proved  that  atmosphere  has  pressure. 
He  noticed  that  an  ordinary  suction  pump  could  not 
lift  water  more  than  thirty-two  feet  and  formulated  the 
theory  that  the  atmosphere  was  not  heavy 
enough  to  push  water  to  a  higher  level. 
Since  mercury  is  thirteen*  times  as  heavy 
as  water,  he  reasoned  that  mercury  could 
only  be  pumped  one  thirteenth  as  high. 
Upon  testing  out  his  conclusions  he  found 
them  to  be  correct. 

Torricelli's  apparatus  was  simply  a  mer- 
curial barometer  similar  to  the  one  de- 
scribed in  this  chapter. 

In  calculating  the  atmospheric  pressure 
on  one  square  inch  of  the  earth's  surface, 
it  is  necessary  simply  to  consider  the 
column  of  mercury  in  the  barometer  as 
having  a  cross  section  of  one  square  inch. 
If  the  mercury'  in  the  tube  stands  at 
twenty-nine  and  one  half  inches,  it  would 
have  a  volume  of  twenty-nine  and  one 

FIG.  74.  — Com-  0.1 

merciai  Mercurial  half  cubic  inches.      Such  an  amount  of 
mercury  weighs  about  14.6  pounds,  which 
is  approximately  the  pressure  of  the  atmosphere  on  each 
square  inch  of  the  earth's  surface. 

Changes  in  Atmospheric  Pressure  due  to  Elevation.  - 
If  a  barometer  is  carried  up  the  side  of  a  mountain,  the 
height  -of  the  mercury  column  will  decrease.     This  is 
because  it  is  only  the   atmosphere   above  which  exerts 
pressure,  and  as  we  go  up  the  side  of  a  mountain  much 


THE  ATMOSPHERE 


77 


FIG.  75.  —  Aneroid  Barometer. 


of  the  atmosphere  is  below  us.     An  ascent  of  one  thou= 

sand  feet  causes  a  lowering  of  about  one  inch  in  the  barom- 
eter column.  Barometers  may 

thus   be   used   to   measure    the 

height  of  the  mountains  or  other 

elevations.     For  convenience  in 

handling,    a    different    type    of 

barometer  is  much  used  for  this 

work.     It  is  called  an  aneroid 

barometer  and  consists  of  a  small, 

flat,  metal  box  from  which  the 

air  has  been  exhausted   (Figure 

75).    A  variation  in  the  pressure 

of  the  atmosphere  causes  a  slight 

change  in  the  shape  of  the  little 

box.  This  change  is  read  on  a  dial  as  atmospheric  pres- 
^_  ^  sure,  in  terms  of  a  column  of  mercury. 
One  half  of  the  atmosphere  is  within  a 
distance  of  less  than  four  miles  of  the 
earth's  surface,  and  the  barometer  read- 
ing at  such  a  height  is  about  fifteen 
inches. 


Experiment  17.  —  Into  a  glass  tube  three 
fourths  of  an  inch  in  diameter  fit  a  plunger 
(Figure  76).  Place  the  bottom  of  the  outer 
tube  in  water  and  raise  the  plunger.  Why  does 
the  water  rise  in  the  tube  ?  In  case  a  common 
glass  pump  is  available  -it  may  be  used  for  this 
experiment. 

Pumps.  —  The  common  pump  (Figure 
77)  removes  the  air  from  the  pump  stock 


FiG.76.-Diagram 
Showing    Action     of 

piston. 


of  the  spout.    The  weight  of  the  water 


78 


GENERAL  SCIENCE 


causes  it  to  flow  through  the  spout.  Notice  the  location 
and  working  of  the  two  valves  in  such  a  pump.  When 
the  piston  is  raised  and  a  partial  vacuum  is  created  in 
the  chamber  of  the  pump,  the  lower  valve  opens  and 
water  is  forced  into  the  chamber.  When  the  piston  is 
lowered,  the  lower  valve  is  closed  by  the  weight  of  the 
water  on  it  and  the  valve  in  the  piston 
opens  and  allows  the  water  to  pass 
through  into  the  chamber  above.  As 
the  piston  is  again  raised  the  piston  valve 
closes  and  the  water  above  it  is  raised  to 
the  level  of  the  spout,  where  it  escapes, 
while  the  lower  valve  is  again  opened 
and  more  water  enters  the  chamber  as 
before.  .V 

In  the  force  pump  (Figure  78)  the  piston 
has  no  valve.  When  the  piston  is  raised, 
a  partial  vacuum  is  created  in  the  cham- 
ber and  the  water  rises  in  the  chamber 
as  it  does  in  the  case  of  the  common 
pump.  When  the  piston  is  lowered,  the 
valve  at  the  bottom  of  the  chamber 
closes  and  the  water  is  forced  out  through 


FIG.  77.  —  Common  the  discharge  valve  into  the  discharge 
suction  Pump.  pipe^nd  into  the  air  chamber.'  The 
pressure  of  the  water  in  the  discharge  pipe  compresses 
the  air  in  the  air  chamber  and  this  pressure  in  turn  causes 
the  water  to  flow  from  the  discharge  pipe  in  a  continuous 
stream.  On  such  a  pump  the  discharge  nozzle  must  be 
smaller  than  the  supply  tube  in  order  to  insure  sufficient 
pressure  to  keep  the  flow  of  water  continuous. 

The  centrifugal  pump  is  a  valveless  pump  which  is 
especially  valuable  where  a  pump  is  needed  which  will 


THE  ATMOSPHERE 


79 


not  be  clogged  by  sand  and  dirt.  Such  a  pump  is  used 
for  pumping  out  the  water  from  coffer  dams  and  swamps, 
and  is  also  much  used  in  city  water  systems.  The  pump 
consists  of  wheel  blades  similar  to  those  of  a  turbine  wheel. 
As  the  wheel  is  turned  rapidly  by  some  power,  the  air 
is  removed  from  the  intake  pipe  and  the  water  is  forced 


FIG.  78.  —  Force  Pump. 


FIG.  79.  —  Section  of  Centrifugal  Pump. 


up  by  atmospheric  pressure  into  the  housing  of  the  wheel. 
The  blades  of  the  wheel  then  force  the  water  out  through 
the  discharge  pipe  (Figure  79). 

The  Siphon. •--  Take  a  short  glass  tube  about  twelve 
inches  long  and  bend  it  into  the  shape  of  the  letter  U, 
with  one  arm  of  the  tube  slightly  longer  than  the  other. 
Fill  the  tube  with  water,  and  then,  holding  the  finger 
over  the  long  end  of  the  tube,  insert  the  other  end  in  a 
jar  of  water  (Figure  80),  letting  the  long  end  hang  over 


80 


GENERAL  SCIENCE 


FIG.  80.  —  Siphon. 

docks  below  the  water  level,  it  is  quite 
common  for  the  laborers  to  work  in  a 
large  steel  chamber  called  a  caisson. 
The  water  is  kept  out  of  the  caisson 
by  air,  which  is  forced  into  it  by  pumps 
with  sufficient  pressure  to  overcome  the 
pressure  of  the  water  outside.  In  the 
more  complex  caissons,  the  entrance  and 
.exit  of  the  workmen  without  allowing 
the  air  to  escape  from  the  caisson  is 
made  possible  by  means  of  air  locks 
which  work  on  the  same  principle  as  the 
water  locks  of  a  canal.  Compressed  air 
can  do  work  in  various  ways.  The  sand 
blast,  the  air  brake,  the  pneumatic 
hammer,  and  the  diving  bell  (Figure  82) 
are  illustrations  of  many  uses. 


the  side  of  the  tumbler.  Can 
you  explain  the  action  of  the 
water  in  this  experiment  ? 

Experiment  18.  —  Fit  a  flask  with 
a  two-hole  rubber  stopper  and  ar- 
range glass  tubing  as  shown  in 
Figure  81.  The  shorter  tube  should 
terminate  in  a  much  smaller  bore 
inside  the  flask,  while  the  longer 
tube  should  just  reach  the  stopper. 
A  little  water  must  be  placed  in  the 
flask  to  start  the  siphon.  How  does 
this  differ  from  the  siphon  in  the 
previous  experiment?  What  deter- 
mines the  force  of  water  in  the  jet? 

Compressed  Air.  —  In  laying 
the  foundations  of  piers  and 


FIG.  81.  —  Another 
Form  of  Siphon. 


THE  ATMOSPHERE 


81 


Oxygen.  —  Carl  Wilhelm  Scheele,  a  Swedish  chemist, 
first  prepared  oxygen  in  1771  by  heating  mercuric  oxide 
and  also  by  other  methods.  On  August  1,  1774,  Joseph 
Priestley,  an  English  experimenter,  without  knowing 
anything  of  Scheele's  work,  obtained  oxygen  by  heat- 
ing mercuric  oxide.  Priestley's  apparatus  consisted  of  a 
bottle  of  mercury  inverted  in 
a  bath  of  the  same  liquid. 
A  little  mercuric  oxide  was 
floated  on  top  of  the  mercury 
in  the  bottle.  He  then  fo- 
cused sunlight  on  the  oxide 
by  means  of  a  burning  lens. 
The  heat  from  the  sunlight 
caused  the  oxide  to  disappear 
and  a  colorless  gas  appeared 
in  its  place.  When  he  intro- 
duced a  glowing  splinter  into 
the  gas,  the  spark  burst  into 
flames.  He  later  put  a  live 
mouse  into  the  gas  and  it  con- 
tinued to  live. 


Scheele  called 

the    gas,    "  Fire     air "     and 
Priestley  called  it "  Good  air." 
Both  of  these  are  appropriate  names,  as  we  shall  soon 
see. 

Although  oxygen  is  one  of  the  chief  constituents  of 
the  air,  we  have  to  use  some  means  of  entrapping  it  before 
we  can  obtain  it  in  its  pure  state.  Oxygen  unites  with 
many  metals,  and  the  compounds  formed  are  the  oxides 
of  the  metals.  We  may  obtain  oxygen  from  many  of  its 
compounds,  but  of  these  potassium  chlorate  is  probably 
the  best  for  laboratory  purposes.  Potassium  chlorate 


FIG.  82.  —  Diving  Bell. 


82 


GENERAL  SCIENCE 


FIG.  83.  —  Preparation  of  Oxygen. 


is  a  white  crystalline  solid  which  gives  off  its  oxygen  when 
sufficiently  heated.  If  manganese  dioxide  or  iron  rust 
is  mixed  with  potassium  chlorate,  it  gives  off  its  oxygen 
more  uniformly  and  at  a  lower  temperature. 

Figure  83  shows  the  arrangement  of  apparatus  for 
preparing  and  collecting  oxygen.  A  test  tube  contains 

the  mixture  of  po- 
tassium chlorate 
and  manganese  di- 
oxide. A  delivery 
tube  leads  from 
the  test  tube  to  a 
pneumatic  trough, 
where  several  bot- 
tles have  previ- 
ously been  filled 
with  water  and 
inverted  ready  for  collecting  the  gas.  Heat  is  then  applied 
to  the  test  tube  and  the  escaping  gas  is  collected  in  the 
bottles  over  water. 

Oxygen  may  also  be  prepared  by  allowing  a  solution 
of  hydrogen  peroxide  to  drop  into  a  flask  containing  some 
crystals  of  potassium  permanganate  covered  with  a 
dilute  solution  of  sulphuric  acid. 

Having  collected  several  bottles  of  oxygen,  we  may 
test  its  properties. 

Experiment  19.  —  Ignite  a  pine  splinter  and  extinguish  the 
flame.  While  it  is  still  glowing  introduce  it  into  one  of  the  bottles 
of  oxygen.  This  was  the  test  used  by  Priestley. 

Experiment  20.  —  By  means  of  a  piece  of  wire  hold  a  small  piece 
of  charcoal  in  the  flame  until  it  is  aglow  and  then  introduce  it 
into  a  bottle  of  oxygen.  It  should  burn  vigorously,  giving  off  a 
brilliant  light.  The  product  is  the  colorless-  gas,  carbon  dioxide. 
If  limewater  is  put  into  the  bottle  in  which  the  charcoal  has  been 


THE  ATMOSPHERE 


83 


burned,  the  limewater  will  look  milky,  due  to  the  insoluble  solid 
which  is  formed  by  the  union  of  the  limewater  and  the  carbon 
dioxide.  Test  the  limewater  with  pure  oxygen  and  air. 

Experiment  21.  —  Iron  may  be  burned  in  oxygen  in  the  follow- 
ing manner  (Figure  84).  Put  enough  sand  into  one  of  the  bottles 
of  oxygen  to  cover  the  bottom 
well  so  that  the  bottle  may  not 
be  broken.  Take  a  piece  of  pic- 
ture wire,  tip  it  with  sulphur,  and 
light  the  sulphur.  Then  put  it 
into  the  bottle  of  oxygen.  The 
burning  sulphur  heats  the  wire  to 
its  kindling  point,  after  which  it 
will  burn  rapidly,  giving  off  a  very 
brilliant  light.  Globules  of  iron 
oxide  are  formed  and  fall  to  the 
bottom  of  the  bottle. 

Experiment  22.  —  The  burn- 
ing of  sulphur  in  oxygen  may 
also  be  tested.  Place  the  sulphur 
in  a  deflagrating  or  combustion 
spoon,  and  after  lighting  it  put  it  into  the  oxygen.  Sulphur  burns 
with  a  blue  flame  in  air,  but  in  oxygen  it  burns  with  a  bright 
violet  flame. 

The  nature  of  oxidation  has  probably  occurred  to  the 
student  by  this  time.  It  is  simply  the  chemical  union 
of  a  substance  with  oxygen,  usually  the  oxygen  of  the 
air.  The  uniting  of  a  substance  with  oxygen  is  called 
the  oxidation  of  the  substance,  and  the  substance  is  said 
to  be  oxidized.  If  the  oxidation  is  so  rapid  that  light 
and  heat  are  evolved,  it  is  called  burning  or  combustion. 
It  was  Lavoisier,  a  French  scientist,  who  first  gave  to 
us  the  explanation  of  combustion.  This  was  in  the  same 
year  and  shortly  after  the  discovery  of  oxygen  by  Priestley. 
A  large  number  of  metals  unite  with  the  oxygen  of  the 
air  to  give  their  oxides.  When  iron  rusts,  it  oxidizes. 


FIG.  84.  —  Burning  Iron  Wire  in 
Oxygen. 


84 


GENERAL  SCIENCE 

• 


Melted  lead  yields  a  yellow  powder  called  lead  oxide. 
Zinc  and  magnesium  burn  brightly  with  the  formation 
of  their  oxides. 

When  a  substance  burns  with  no  flame,  there  is  no  gas 
evolved,  since  a  flame  is  burning  gas.  Hard  coal  burns 
with  much  less  flame  than  soft  coal,  indicating  the  ab- 
sence of  gaseous  materials  in  the  hard  coal.  Coke  and 
charcoal  are  coal  and  wood  respectively  without  their 
gases,  which  have  been  driven  off  by  heat. 

Experiment  23.  —  Place  a  lighted  candle  in  a  shallow  basin  and 
then  lower  a  tall  slender  lamp  chimney  over  the  candle,  supporting 

the  chimney  by  two  pieces  of 
wood  so  that  the  free  passage 
of  air  at  the  bottom  of  the 
chimney  may  not  be  ob- 
structed. Now  pour  water  in 
the  basin  until  the  bottom  of 
the  chimney  is  covered  and 
note  the  action  of  the  flame 
(Figure  85). 

Oxygen    and    Life.  — 

FIG.    85. —  The    candle   flame    will   be  '    . 

extinguished   when  the  supply  of  air  is    Oxygen   IS    the    llfe-glVing 

principle   in    the    animal 

and  vegetable  kingdoms,  and  an  abundant  supply  of  it  is 
necessary  for  the  sustenance  of  life.  Neither  plants  nor 
animals  can  live  without  it.  Plants  take  oxygen  from 
the  air  through  their  leaves,  while  the  animals  usually 
have  special  organs  for  the  purpose  of  separating  the 
oxygen  from  the  air.  The  process  of  obtaining  oxygen 
from  the  air  by  plants  and  animals  is  called  respiration, 
which  consists  both  of  breathing  and  oxidation  in  the 
tissues.  In  the  higher  animals  the  oxygen  is  taken 
directly  into  the  lungs,  where  by  osmosis  it  reaches  the 
blood  and  is  then  carried  to  all  parts  of  the  body  by 


THE   ATMOSPHERE 


85 


the  corpuscles  of  the  blood.  The  purpose  of  respiration 
is  to  oxidize  the  materials  of  the  body  that  are  constantly 
wearing  out  into  a  form  of  waste  that  may  be  removed 
from  the  body  more  readily. 

The  results  of  oxidation  in  the  body  are  :  energy,  which 
is  created  in  the  form  of  heat ;  carbon  dioxide,  formed  as 
a  result  of  the  union  of  the  carbon  in  the  waste  products 
with  oxygen ;  and  waste  matter,  in  forms  which  may 
be  easily  'disposed  of.  Part  of  the  heat  energy  is  used 
in  the  body  and  part  of  it  escapes  as  heat.  This  oxi- 
dation of  the  body  is  constantly  changing  it. 

Nitrogen.  —  Air  is  approximately  one  fifth  oxygen 
and  four  fifths  nitrogen.  Oxygen  cannot  be  taken  di- 
rectly from  the  air.  Nitrogen,  however,  may  be  obtained 
from  the  air  by  burning 
out  the  oxygen  from  a 
limited  quantity  of  it. 

Experiment  24.  —  Place  a 
small  quantity  of  red  phos- 
phorus on  a  slice  of  cork. 
Support  the  cork  by  a  wire 
held  upright  by  sticking  it  into 
a  large  rubber  stopper.  Place 
in  a  pan  and  surround  by  two 
inches  of  water  (Figure  86). 

Light  the  phosphorus  and  place  over  it  a  quart  jar.  Water  will 
rise  in  the  jar  as  the  oxygen  is  used  in  the  combustion  of  the 
phosphorus.  When  the  white  smoke,  phosphorus  oxide,  has  dis- 
solved in  the  water,  slip  a  piece  of  glass  under  the  jar  and  set  it 
upright  on  the  table.  Test  the  nitrogen  in  a  number  of  ways  in 
which  oxygen  was  tested. 

Nitrogen  does  not  readily  unite  with  other  elements. 
Its  principal  value  in  the  air  is  to  dilute  the  oxygen,  which 
would  otherwise  be  too  active  for  many  of  its  uses.  Nitf o- 


FIG.  86. 


86 


GENERAL  SCIENCE 


gen  has  neither  color,  odor,  nor  taste.  Due  to  the  fact 
that  it  unites  so  reluctantly  with  other  elements,  it  is 
used  in  all  of  our  common  explosives,  such  as  gunpowder, 
dynamite,  and  nitroglycerine. 

Nitrogen  has  a  very  important  work  to  do  in  the  man- 
ufacture of  proteins  by  the  plants,  but  just  how  this 
takes  place  is  not  well  known.  The  plant  seems  to  add 

nitrogen  and  other  elements 
to  the  carbohydrates.  These 
foods  are  taken  into  the 
plants  in  the  form  of  solu- 
tions in  ground  water,  but 
there  are  a  few  plants  that 
seem  to  take  up  nitrogen  di- 
rectly from  the  air.  These 
are  such  plants  as  beans, 
peas,  alfalfa,  and  clover.  This 
power  is  due  to  certain  bac- 
teria or  very  small  plants 
which  attach  themselves  to 
the  roots  (Figure  87)  and, 
taking  the  nitrogen  from  the 
air,  build  it  into  certain 
albuminous  foods  which  the  plant  can  use.  The  growing 
of  crops  of  peas,  beans,  clover,  and  alfalfa  is  very  bene- 
ficial to  the  soil,  since  these  little  bacteria  take  more 
nitrogen  from  the  air  than  the  plants  to  which  they  are 
attached  need,  and  therefore,  when  the  plant  dies,  an 
excess  of  valuable  nitrogen  is  left  in  the  soil  for  other 
plants  to  use.  Farmers  often  grow  such  crops  simply 
for  the  purpose  of  enriching  soil  which  has  become  im- 
poverished through  the  raising  of  other  crops.  Artificial 
fertilizers  which  contain  nitrogen  compounds  are  also 


FIG.  87.  —  Roots  showing  Nitrogen 
Tubercles. 


THE  ATMOSPHERE  87 

much  used  for  this  purpose.  The  greatest  supply  of 
available  nitrogen  for  use  in  commercial  fertilizers  and 
explosives  is  found  in  Chile  in  the  form  of  Chile  salt- 
peter, which  is  mined  in  great  quantities  and  exported 
to  all  parts  of  the  world. 

•Protein  is  one  of  the  necessary  foods  of  animals,  and 
since  they  cannot  make  their  own  protein,  the  animals 
must  get  it  from  the  plants.  Plants  make  protein 
from  nitrogen  and  other  elements  such  as  carbon  and 
oxygen,  and  this  in  turn  becomes  natural  food  for 
animals. 

Air,  a  Mixture.  —  We  are  now  able  to  answer  the 
question  as  to  whether  air  is  a  chemical  compound  of 
nitrogen  and  oxygen  or  simply  a  mixture  of  the  two  gases. 
We  can  do  this  by  comparing  the  properties  of  nitrogen 
and  oxygen  with  those  of  air.  The  properties  of  air 
are  simply  those  of  oxygen  modified  by  those  of  nitrogen. 
For  example,  air  supports  the  combustion  of  other  sub- 
stances in  the  same  way  that  oxygen  does  but  much  less 
energetically,  because  the  nitrogen  interferes  by  dilut- 
ing the  oxygen.  We  have  already  compared  the  burning 
of  sulphur  in  air  with  its  burning  in  pure  oxygen.  Since 
only  about  one  fifth  of  air  is  oxygen,  a  substance  burned 
in  air  is  supplied  with  oxygen  only  about  one  fifth  as 
fast  as  when  burned  in  pure  oxygen.  If  air  were  a  chemi- 
cal compound,  its  properties  would  in  all  probability 
be  very  different  from  those  of  the  two  gases  which  com- 
pose it.  Another  proof  is  that  the  weight  of  the  air 
may  be  calculated  by  calculating  the  weight  of  each  gas 
separately  in  the  proportion  of  four  of  nitrogen  to  one  of 
oxygen.  In  100  liters  of  air  there  are  79  liters  of  nitrogen 
which  will  weigh :  • 

1.257  X  79  =  99.3  grams 


88 


GENERAL  SCIENCE 


The  weight  of  the  oxygen  will  be : 

1.43  X  21   =30  grams 
99.3     +  30  =  129.3  grams,  the  weight  of  100  liters  of  air. 

This  result  agrees  with  that  obtained  by  actually  weigh- 
ing the  air.  All  four  results  indicate  that  air  is  simply 
a  mixture  of  these  two  gases. 

Respiration.  —  Respiration  serves  two  purposes  :  that 
of  bringing  oxygen  to  the  blood  and  removing  carbon 
dioxide  from  the  blood.  As  the  blood  exchanges  food 
and  oxygen  for  the  wastes  of  the  tissues,  it  gradually 
becomes  laden  with  these  waste  products  which  must 
be  removed  by  the  different  organs  of  excretion.  Some 

of  them  are  removed  by  the 
kidneys,  some  by  the  skin, 
while  the  carbon  dioxide  is 
removed  by  the  lungs.  The 
chief  organs  of  breathing  or 
respiration  are  the  lungs  and 
air  passages. 

The  Lungs.  -  -  The  lungs 
are  two  pinkish  gray  organs 
of  light,  spongy  appearance 
(Figure  88).  They  are  lo- 
cated in  the  chest  cavity. 
Each  lung  is  surrounded 
with  two  layers  of  an  elastic,  serous  membrane,  called 
the  pleura.  One  layer  closely  covers  the  lung,  while  the 
other  is  attached  to  the  wall  of  the  chest  in  such  a  way  as 
to  form  a  closed  sac.  As  the  lungs  change  in  size  these 
two  layers  glide  on  each  other  with  little  friction.  Pleu- 
risy is  an  inflammation  of  this  membrane  due  to  the 
cessation  of  the  lubricating  serum. 


FIG.  88.— The  Lungs. 


THE  ATMOSPHERE  89 

The  lungs  are  composed  of  combinations  of  air  sacs  or 
air  cells  which  are  grouped  around  the  numerous  small 
subdivisions  of  the  bronchial  tubes.  These  air  sacs 
are  composed  of  a  thin  elastic  outer  layer  of  connective 
tissue  and  a  lining  of  mucous  membrane.  Between 
these  two  layers  the  minute  thin-walled  capillaries  are 
located.  The  blood  here  is  separated  from  the  air  only 
by  thin  walls  of  the  capillaries  and  the  mucous  mem- 
brane lining  the  air  sacs. 

The  Air  Passages.  —  Air  enters  the  body  through 
the  mouth  or  nose  and  passes  through  the  pharynx  and 
larynx  into  the  windpipe  or  trachea.  The  trachea  is 
a  tube  about  three  fourths  of  an  inch  in  diameter  and 
about  four  inches  long.  Its  walls  are  strengthened  by 
rings  of  cartilage.  The  trachea  divides  at  its  lower 
end  into  two  branches  called  the  bronchial  tubes.  These 
subdivide  and  finally  terminate  in  the  tiny  air  sacs.  The 
tubes  and  lungs  are  lined  throughout  with  a  mucous 
membrane.  The  entrance  to  the  larynx  and  trachea 
is  guarded  by  the  epiglottis,  which  stands  open  to  admit 
air.  As  food  is  forced  back  in  the  act  of  swallowing  it 
strikes  the  epiglottis  and  closes  it  over  the  trachea, 
forming  a  bridge  over  which  the  food  passes  into  the 
gullet. 

Mechanism  of  Breathing.  —  Breathing  involves  two 
processes,  inhaling  or  inspiration  and  exhaling  or  expira- 
tion. Inhaling  consists  of  drawing  the  air  through  the 
various  parts  of  the  lungs  to  the  air  sacs.  Exhaling  is 
simply  the  reverse  of  this  process.  The  diaphragm 
forms  a  movable  floor  to  the  chest  cavity  and  draws 
air  into  the  lungs.  The  air  is  really  forced  into  the  lungs 
by  the  air  pressure,  to  relieve  the  partial  vacuum  that 
has  been  created.  When  the  diaphragm  relaxes,  it  returns 


90  GENERAL  SCIENCE 

to  its  normal  position  and  forces  air  from  the  lungs  by 
reducing  the  size  of  the  chest  cavity. 

A  conscious  effort  should  be  made  occasionally  to  take 
an  increased  amount  of  air  into  the  lungs,  "  deep  breath," 

since  by  so  doing  a  larger  portion  of 

the  lungs  will  be  used. 

Experiment  25.  —  Tie  a  rubber  bag  par- 
tially filled  with  air  to  one  end  of  a  glass  tube 
and  arrange  the  tube  in  a  bell  jar  as  shown  in 
Figure  89.  A  diaphragm  for  the  bell  jar  may 
be  made  by  gluing  a  piece  of  leather  with  a 
string  through  it  to  a  piece  of  sheet  rubber. 
As  the  diaphragm  is  pulled  down,  the  rubber 
bag  inside  the  bell  jar  will  increase  in  size. 
Why?  Does  it  return  to  its  former  size  when 
the  diaphragm  is  allowed  to  go  back  to  its 
FIG.  89.  normal  position? 

Mouth  Breathing.  -  -  The  proper  passage  for  the  air 
to  the  lungs  in  breathing  is  through  the  nose.  When  air 
is  inhaled  through  the  nose,  it  is  warmed  before  it  reaches 
the  delicate  tissues  of  the  throat  and  lungs.  The  moist- 
ened hairs  of  the  nose  also  remove  dust  particles  and 
disease  germs  before  they  reach  places  where  serious 
injury  may  be  done. 

The  habit  of  mouth  breathing  is  a  bad  one  for  a  num- 
ber of  reasons,  (a)  The  dust  and  germs  are  not  removed 
in  the  mouth  as  in  the  nose  by  the  hairs  and  folds  of 
mucous  membrane.  (6)  The  air  reaches  the  lungs  before 
it  is  properly  warmed,  (c)  Mouth  breathing  hinders 
the  normal  development  of  the  upper  jaw  and  destroys 
the  natural  beauty  of  the  face. 

With  practice  we  can  acquire  the  habit  of  nose  breath- 
ing even  when  exercising  violently.  Trainers  of  athletes 
are  careful  to  cultivate  this  habit,  since  mouth  breathing 


THE  ATMOSPHERE  91 

always  places  a  contestant  for  athletic  honors  at  a  great 
disadvantage. 

Adenoids.  —  Occasionally  small  bulbous  growths  par- 
tially fill  the  nasal  passages  leading  to  the  throat.  These 
growths  are  called  adenoids.  A  good  surgeon  can  readily 
remove  them.  This  should  always  be  done,  since  mouth 
breathing  is  such  a  serious  menace  to  health. 

Colds  are  inflammations  of  the  membranes  lining  the 
air  passages.  If  the  area  affected  is  limited  to  the  nasal 
cavities,  we  call  the  inflammation  a  cold  in  the  head ; 
if  the  pharynx  is  affected,  a  sore  throat  is  the  result ;  if 
the  trachea  and  bronchial  tubes  are  affected,  we  call  it  a 
chest  cold.  When  the  inflammation  extends  to  the  lining 
of  the  air  sacs,  pneumonia  results. 

Diphtheria,  croup,  and  tuberculosis  are  all  germ  diseases 
which  are  produced  by  special  kinds  of  bacteria. 

QUESTIONS 

1.  Who  was  Torricelli? 

2.  Why  is  the  air  less  dense  on  the  top  of  a  mountain  than 
that  at  its  base? 

3.  What  would  be  some  of  the  effects  of  increasing  the  amount 
of  oxygen  in  the  air? 

4.  How  can  you  show  that  exhaled  breath  contains  carbon 
dioxide? 

5.  How  does  painl  prevent  iron  from  rusting? 

6.  What  is  the  working  principle  of  the  ordinary  commercial 
fire  extinguisher? 

7.  Why  does  a  good  draft  make  a  fire  burn  better? 

8.  Why  do  we  use  kindling  in  starting  a  coal  fire  ? 

9.  Why  does  a  blanket  thrown  over  a  fire  put  it  out? 

10.  What  causes  wood  to  rot? 

11.  What  is  the  value  of  nitrogen  in  the  air? 

12.  Give  some  proofs  that  air  has  "  inertia." 

13.  Of  what  value  are  breathing  exercises? 


92  GENERAL  SCIENCE 

14.  Do  babies  breathe  through  the  nose  or  mouth? 

15.  What  should  be  done  when  children  are  found  to  have  the 
habit  of  mouth  breathing? 

16.  How  does  dust  affect  the  normal  functioning  of  the  lungs? 

17.  Why  are  mouth  breathers  more  susceptible  to  contagious 
diseases? 

18.  Is  breathing  voluntary  or  involuntary? 

19.  In  what  respects  does  exhaled  air  differ  from  inhaled  air? 


CHAPTER  VI 


WATER 

WATER  is  not  an  element  like  oxygen,  nor  is  it  a  mixture 
such  as  we  have  found  air  to  be,  but  a  compound  of  two 
elements,  hydrogen  and  oxygen.  Water  as  it  occurs 
in  nature  usually  has  a  number  of  other  substances,  such 
as  limestone,  different  salts,  and  carbon  dioxide,  dissolved 
in  it ;  but  pure  water  is  composed  of  only 
the  two  substances  named  above. 

It  is  quite  easy  to  separate  water  into 
the  elements  which  compose  it  by  elec- 
trolysis, which  means  "  breaking  apart  " 
or  analysis  by  the  aid  of  electricity. 

Electrolysis  of  Water.  -  -  The  commer- 
cial piece  of  apparatus  sold  for  this  ex- 
periment is  called  a  Hoffmann  apparatus 
(Figure  90).  However,  if  such  an  appa- 
ratus is  not  available,  the  experiment 
may  be  performed  very  well  by  such  an 
apparatus  as  shown  in  Figure  91.  The 
water  used  should  be  slightly  acidulated 
with  sulphuric  acid,  and  the  wires  leading  from  the  bat- 
tery should  terminate  in  platinum  foil.  The  ends  of  the 
wires  are  called  poles  or  electrodes.  The  test  tubes  are 
filled  with  water  and  suspended  over  the  electrodes  so 
that  the  mouths  of  the  test  tubes  shall  be  below  the  level 
of  the  water  in  the  pan.  The  amount  of  electricity  needed 


FIG.  90.—  Hoffmann 
Apparatus. 


94  GENERAL  SCIENCE 

will  be  at  least  as  much  as  that  furnished  by  four  dry 
cells,  and  six  or  eight  cells  will  be  better  to  hasten  the 
action.  It  requires  much  energy  to  electrolyze  water, 
since  the  union  of  the  two  gases  is  a  strong  one.  When 
the  batteries  are  attached,  a  current  will  pass  through 

the  wires  and  the  water, 

oxygen         Hydrogen  and  little  bubbles  of  gas 

will  be  seen  arising  from 
each  electrode.  The  sul- 
phuric acid  furnishes  the 
passageway  for  the  cur- 
rent between  the  elec- 

FIG.  91.— -An 'Easily  Constructed  Appa-    trodeS.      It  will  be  noticed 

that  the  gas  is  evolved 

from  one  electrode  much  faster  than  from  the  other.  Test 
with  a  glowing  splinter  the  gas  in  the  tube  which  has  the 
least  gas  in  it.  What  gas  that  you  have  studied  does  it 
resemble?  Test  the  gas  in  the  other  tube  with  a  flame. 
This  gas  is  hydrogen,  which  we  shall  soon  study  more 
fully.  The  other  gas  is  of  course  oxygen.  What  is  the 
approximate  proportion  of  the  volumes  of  the  two  gases  ? 
Hydrogen  is  so  named  because  it  helps  to  form  water, 
the  Greek  word  for  water  being  Hydor.  Mention  some 
other  English  words  in  which  this  name  appears. 

Water  by  Synthesis.  —  If  the  gases  secured  in  the  pre- 
ceding experiment  are  mixed  in  the  same  proportion 
in  a  tube  over  mercury  and  exploded  by  an  electric 
spark,  the  result  will  be  water.  The  proportion  of  oxygen 
to  hydrogen  should  be  one  volume  of  oxygen  to  two  of 
hydrogen.  Simply  mixing  these  gases,  however,  will  not 
produce  water.  The  temperature  must  be  high  enough 
(620°  C.)  to  cause  action  between  them.  A  slight  ex- 
plosion is  the  evidence  of  such  chemical  action. 


WATER  95 

Physical  and  Chemical  Changes.  —  If  we  throw  some 
water  into  the  air,  it  will  fall  to  the  ground,  but  the  com- 
position of  the  water  is  not  changed.  It  is  still  water. 
The  water  of  the  ocean  is  changed  to  vapor  and  carried 
long  distances  by  winds,  to  'fall  again  as  water  in  the  form 
of  rain  or  snow,  but  it  is  water  during  the  entire  change 
of  location.  These  changes  are  called  physical  changes. 
In  the  experiment  we  have  just  performed,  however,  we 
have  a  different  kind  of  change.  The  result  was  no  longer 
water  but  two  substances  of  entirely  different  character  : 
one  of  them  a  strong  supporter  of  burning  or  combustion, 
and  the  other  a  substance  which  will  burn.  How  dif- 
ferent from  water  which  is  so  much  used  to  extinguish 
flames !  The  electrolysis  of  water  is  a  chemical  change. 
If  we  place  a  piece  of  paraffin  in  an  evaporating  dish  and 
apply  heat  to  it,  a  change  will  take  place  in  the  paraffin. 
It  melts  and  becomes  a  liquid,  but  the  substance  is  still 
paraffin  and  possesses  the  same  properties  as  it  did  before, 
with  the  addition  of  the  ordinary  properties  of  liquids. 
A  change  which  does  not  alter  the  nature  or  properties 
of  a  substance,  but  only  the  form  or  appearance,  is  called 
a  physical  change.  A  chemical  change  is  one  in  which 
the  properties  are  changed  and  an  entirely  new  substance 
is  formed.  When  ice  is  changed  to  water  or  water  to  ice, 
is  there  any  change  in  the  real  nature  of  the  substance  ? 
What  kind  of  change  is  vaporization?  Burn  a  piece  of 
wood.  What  kind  of  change  is  demonstrated  here? 

Experiment  26.  —  Into  a  test  tube  pour  a  little  solution  of  ordi- 
nary table  salt  and  in  another  test  tube  a  similar  amount  of  silver 
nitrate  solution.  Note  the  appearance  of  each.  Now  pour  the 
contents  of  one  tube  into  the  other.  The  solid  that  slowly  falls 
to  the  bottom  of  the  tube  is  called  a  precipitate.  What  kind  of 
change  is  this? 


96 


GENERAL  SCIENCE 


If  a  piece  of  iron  is  exposed  to  the  weather,  it  rusts  and 
a  reddish  substance  is  formed.  The  iron  is  slowly  oxi- 
dized. What  kind  of  change  is  this? 

Preparation  of  Hydrogen.  -  -  The  electrolysis  of  water 
taught  us  that  water  is  composed  of  two  gases  —  oxygen 
and  hydrogen.  One  of  these  gases  we  have  studied  so 
that  we  are  quite  welt  acquainted  with  its  properties. 
It  now 'remains  for  us  to  study  the  properties  of  the  other 
gas  in  which  we  are  so  vitally  interested.  Hydrogen  is 
another  element  which  as  a  component  of  water  is  found 

in  all  the  tissues 
of  the  body  and 
therefore  is  abso- 
lutely essential  to 
life. 

Hydrogen  may 
be  easily  prepared 
by  bringing  to- 
gether certain  acids 
and  metals.  All 
acids  contain  hydrogen,  but  the  best  acids  for  our  pur- 
pose are  dilute  sulphuric  acid  and  dilute  hydrochloric 
acid.  The  apparatus  needed  for  the  preparation  of  hydro- 
gen is  shown  in  Figure  92. 

Experiment  27.  —  Into  a  wide-mouthed  pint  bottle  intro'duce  a 
handful  of  zinc.  Use  a  two-hole  rubber  stopper  in  this  bottle 
and  through  one  hole  pass  a  thistle  tube  reaching  nearly  to  the 
bottom  of  the  bottle.  Through  the  other  pass  a  delivery  tube 
leading  to  a  pneumatic  trough.  Pour  the  dilute  acid  through  the 
thistle  tube  and  collect  the  gas  formed  over  water  as  in  the  case 
of  oxygen.  The  first  gas  evolved  is  always  mixed  with  air  and 
should  not  be  used. 

To  determine  whether  the  gas  is  nearly  pure,  collect  some  of 
it  in  a  small  test  tube  and  carry  it  mouth  downward  to  a  flame  a 


'  FIG.  92.  —  Collecting  Hydrogen. 


WATER 


97 


few  feet  away.  When  the  hydrogen  in  the  test  tube  does  not  ex- 
plode but  burns  slowly  up  the  tube,  the  gas  is  pure  enough  to  be 
collected. 

Properties  of  Hydrogen.  —  Hydrogen  is  the  lightest 
known  substance,  weighing  only  one  sixteenth  as  much 
as  oxygen.  A  liter  of  hydrogen  weighs  .09  gram.  Like 
oxygen  and  nitrogen,  hydrogen  is  a  colorless,  odorless, 
and  tasteless  gas.  In  testing  the  gas  for  its  purity,  it 
was  noticed  that  the  less  the  quantity  of  air  mixed 
with  it  the  less  violent  the  explosion ;  and  we  learned 
also  that  hydrogen  would  burn.  However,  if  we  desire 
to  burn  hydrogen 
in  a  jet,  we  must 
exercise  some  care 
in  lighting  it  in 
order  to  avoid  the 
possibility  of  a 
dangerous  explo- 
sion. Arrange 
the  apparatus  as 
shown  in  the  dia-  FlG-  93'  ~ Burning  Hydrosen- 

gram  (Figure  93).  In  lighting  the  gas  it  is  well  to 
use  a  test  tube  in  the  following  manner.  Hold  the 
tube  over  the  jet  for  a  minute  and  .then  carry  it  mouth 
downward  to  a  flame  several  feet  away.  When  the 
gas  in  the  test  tube  burns  slowly  enough  that  we  may 
carry  it  back  and  light  the  jet  with  it,  the  hydrogen  is 
pure  enough  to  be  safe. 

Hydrogen  burns  with  a  very  hot,  colorless  flame,  with 
the  formation  of  water.  To  test  this,  hold  a  dry  beaker 
or  evaporating  dish  over  the  flame  and  note  the  result. 
The  same  result  may  have  been  noticed  when  the  hydro- 
gen was  exploded  in  the  test  tube. 


98 


GENERAL  SCIENCE 


Experiment   28.  —  Bring   a   bottle   of   pure   hydrogen   over   a 
lighted  candle.     Notice  that  the  gas  takes  fire  at  the  mouth  of 

. .       the    bottle    and    burns    quietly, 

while  the  flame  on  the  candle  is 
extinguished  as  the  bottle  is 
further  lowered.  Remove  the 
bottle  slowly  and  the -candle  will 
be  relighted  as  the  wick  passes 
through  the  burning  hydrogen 
(Figure  94). 

The  most  important  prop- 
erty of  hydrogen  is  its  com- 
bustibility. The  flame  is 
exceedingly  hot,  but  not  very 
luminous.  When  it  burns  in 

FIG.  94.  — Hydrogen  burns  but  does     pure  oxygen,  it  is  the  hottest 

not  support  combustion.  11/1 

ot  all  names,  burning  at  a 

temperature  of  nearly  4000°  C.  It  is  much  used  in  the 
melting  of  certain  metals  and  the  cutting  of  steel.  A  six- 
inch  shaft  of  solid  steel  has  been  cut  in  less  than  forty 
seconds  with  such  a  flame  (Figure  95). 

Three  States  of  Water.  —  Water  occurs  quite  commonly 
in  all  three  states  of  matter  —  solid,  liquid,  and  gaseous. 
The  liquid  form  is  most  common  and  the  name  "  water  " 
is  usually  applied  to  this  state;  however,  when  water 
is  vaporized  or  when  it  freezes  and  becomes  a  solid,  it 
does  not  cease  to  be  water.  The  water  that  is  contained 
in  the  air  is  sometimes  called  "  water  vapor  "  or  steam, 
while  the  solid  form  is  called  ice. 

Freezing  of  Water.  -  -  The  temperature  at  which  water 
freezes  is  definite  and  under  ordinary  circumstances  is 
always  the  same.  On  the  Centigrade  thermometer  the 
freezing  point  of  water  is  taken  as  the  starting  point  in 
making  the  scale  and  is  called  zero.  On  the  Fahrenheit 


WATER 


99 


thermometer  the  freezing  point  is  taken  as  thirty-two 
degrees. 

If  an  apparatus  is  arranged  such  as  is  shown  in  Figure 
96,  it  will  be  found  that  as  the  water  in  the  flask  is  heated 


FIG.  95.  —  Cutting  Heavy  Steel  Plate  with  Oxy-acetylene 
Flame. 


the  water  in  the  tube  will  move  up,  due  to  the  expansion 
of  the  water.  If  on  the  other  hand  the  water  in  the 
flask  be  cooled,  the  water  in  the  tube  will  move  down, 
showing  that  the  water  in  the  flask  is  contracting.  As 
the  water  is  further  cooled  the  contraction  oontinues 


100  GENERAL  SCIENCE 

until  a  temperature  of  4°  C.  is  reached,  when  the  water 
begin,  to  expand  again,  and  as  it  approaches  the  freezing 
point  becomes  much  lighter  than  water  at  higher  tem- 
peratures. As  water  is  cooled  after  it  becomes  ice 
it  contracts  like  ordinary  solids,  but  it  never  contracts 
enough  so  that  its  volume  is  as  small  as  when  it  was  a 
liquid.  Since  ice  is  lighter  than  water,  it  floats 
on  water  and  forms  a  covering  which  prevents 
the  water  beneath  it  from  freezing,  thus  keep- 
ing it  habitable  for  fish  and  other  sea  animals, 
even  in  the  coldest  regions. 

If  water  is  cooled  until  the   temperature 
reaches  zero,  ice  will  begin  to  form.     As  cold 
is  further  applied,  no  change  in  temperature 
will  be  noticed  until  the  whole  mixture  is 
frozen,  when  the  temperature  will  again  begin 
to  fall.     The  freezing  point  of  water  may  be 
lowered  by  dissolving  salts  of  various  sorts  in 
it.     The  water  of  the  ocean  freezes  at  a  lower 
temperature  than  the  still  water  of  our  inland  lakes.    Can 
you  think  of  a  reason  why  this  is  so? 

Steam.  —  When  water  is  sufficiently  heated,  it  changes 
to  steam.  The  steam  rises  through  the  water  in  bubbles 
and  escapes  at  the  surface  into  the  air.  When  the  forma- 
tion of  these  bubbles  occurs  rapidly,  the  water  is  said  to 
boil.  The  temperature  at  which  boiling  begins  is  called 
the  boiling  point.  On  the  Centigrade  scale  this  point  is 
100°.  On  the.  Fahrenheit  it  is  212°.  However,  this 
point  varies  with  the  air  pressure.  As  the  pressure  on  the 
surface  of  the  liquid  is  decreased,  the  temperature  of  the 
boiling  point  is  lowered.  This  change  is  readily  noticed 
in  ascending  mountains.  On  the  top  of  Mont  Blanc 
the  boiling  point  of  water  is  84°  C.  Water  in  Denver 


WATER  101     -•• 


boils  at  95°,  in  Quito  at  90°.  It  would  be  possible- to' 
the  height  of  elevations  by  a  determination  made  from 
the  boiling  of  water.  What  would  be  the  effect  of  high 
altitudes  on  the  cooking  of  such  foods  as  are  prepared 
by  boiling? 

We  have  stated  that  liquids  have  a  definite  boiling 
point  under  ordinary  conditions.  However,  water  will 
pass  into  vapor  at  any  temperature.  Even  ice  and  snow 
evaporate  or  change  to  vapor  directly,  without  passing 
through  the  intermediate  stage,  water.  This  vapor 
exerts  a  definite  pressure  which  may  be  measured,  but  it 
is  very  small  at  the  lower  temperatures.  As  the  tem- 
perature of  the  water  rises,  the  pressure  of  the  vapor  or 
steam  increases  until,  at  the  boiling  point,  it  has  a  pres- 
sure equal  to  the  pressure  of  the  atmosphere,  which  we 
have  studied  in  terms  of  a  column  of  mercury.  If  the 
steam  cannot  then  escape  and  the  heating  of  the  water 
is  continued,  the  pressure  increases  enormously  until 
in  large  volumes  it  is  able  to  do  a  vast  amount  of 
work,  such  as  pulling  a  heavily  loaded  train  of  many  cars. 

When  water  changes  to  steam,  it  increases  enormously 
in  volume  and  of  course  becomes  correspondingly  lighter. 
Steam  is  colorless,  but  when  it  escapes  into  the  air  there 
is  always  a  white  cloud  which  is  sometimes  called  steam. 
This  cloud  is  not  steam,  but  is  produced  by  little  particles 
of  water  caused  by  the  condensation  which  takes  place 
when  the  hot  steam  comes  in  contact  with  the  colder 
atmosphere. 

Solutions.  —  Salt  dissolves  in  water.  That  is,  when 
salt  is  thrown  into  water,  it  disappears  slowly,  if  left 
to  itself  in  the  water,  and  more  rapidly  if  the  water  is 
shaken.  A  solid  which  behaves  in  this  way  when  thrown 
into  a  liquid  is  said  to  be  soluble  in  that  liquid.  The 


102  GENERAL  SCIENCE 

M-quid  is*  Called  the  solvent  and  the  solid  the  solute.  Of 
course  the  salt  did  not  really  disappear.  Invisible 
particles  of  it  are  held  in  the  water,  as  is  shown  by  the 
fact  that  the  water  tastes  salty.  The  salt  water  obtained 
is  called  a  solution.  If  the  solid  is  some  other  color  than 
white,  the  water  solution  of  it  will  be  colored ;  but  the 
solution  will  always  be  clear  even  if  colored.  An  insoluble 
substance  like  starch,  powder,  lime,  or  clay  can  be  scat- 
tered through  the  water  by  shaking,  but  the  mixture 
will  be  turbid.  Such  a  mixture  of  a  solid  and  a  liquid 
is  called  a  suspension.  If  allowed  to  stand  long  enough, 
the  suspended  material  will  settle  to  the  bottom,  leaving 
the  liquid  clear.  In  the  case  of  a  solution,  however, 
there  is  no  settling  of  the  solute. 

If  we  continue  to  add  salt  to  a  definite  volume  of  water, 
there  will  come  a  time  when  the  salt  is  no  longer  dissolved. 
The  solution  is  then  said  to  be  saturated,  and  if  more 
salt  is  added,  it  simply  falls  to  the  bottom.  100  grams 
of  water  at  0°  C.  will  dissolve  35.5  grams  of  salt  and  no 
more.  If  the  water  is  heated,  the  amount  of  salt  that 
it  will  dissolve  is  increased  slightly.  In  the  case  of  some 
solids,  the  effect  of  heating  the  water  is  more  marked  than 
with  salt. 

Tinctures  are  solutions  in  which  alcohol  is  the  solvent. 

Properties  of  Solutions.  —  As  we  have  stated  before, 
the  taste  and  color  of  the  solutes  are  imparted  to  the 
solution.  A  small  bit  of  potassium  permanganate  will 
be  sufficient  to  color  a  large  quantity  of  water.  As  a 
usual  thing  it  will  be  found  that  as  water  dissolves 
salts,  the  volume  will  increase,  and  it  will  be  found  that 
the  water  has  been  otherwise  changed.  It  boils  at  a 
higher  temperature  than  it  did  before,  and  freezes  at  a 
lower  temperature ;  a  saturated  solution  of  common  salt 


JTIG    97.  —  Some  Forms  of  Crystals. 

The  mineral  species  are  named  from  left  to  right  for  each  of  the  four  rows :  — 
1.  Quartz.         2.  Zircon.         3.  Fluorite.         4.   Garnet. 

5.  Quartz.        6.   Rock  salt. 
7    Gypsum.         8.   Quartz.         9.   Calcite. 

10    Emerald.         11.  Gypsum.          12.   Topaz.          13.  Staurolite. 

103 


104  GENERAL  SCIENCE 

boiling  at  about  108°  C.  and  freezing  at  -21°  C.  The 
density  of  a  salt  solution  should  be  tested  to  determine 
whether  it  is  different  from  that  of  pure  water. 

Experiment  29.  —  Into  a  vessel  containing  some  pure  water  at 
about  the  temperature  of  the  room,  place  a  thermometer  and  note 
the  exact  temperature.  Next  add  some  ammonium  nitrate  and 
again  read  the  temperature  from  the  thermometer. 

This  is  the  usual  effect  of  dissolving  solids  in  water. 

After  salt  has  been  dissolved  in  water,  how  may  it  be 
recovered  ? 

Water  of  Crystallization. — When  a  substance  crys- 
tallizes, it  takes  up  water  which  is  known  as  water  of 
crystallization.  If  we  place  a  few  crystals  of  copper  sul- 
phate in  an  evaporating  dish  and  heat  them,  they  will 
change  to  a  grayish  blue  powder.  This  substance  may 
be  recrystallized  by  dissolving  it  in  water  and  allowing 
the  water  to  evaporate  slowly.  If  sodium  sulphate  is 
placed  in  a  test  tube  and  heated,  it  will  be  dissolved  in  its 
own  water  of  crystallization. 

Each  substance  has  its  own  crystalline  form.  For 
example,  salt  crystals  are  cubical  in  shape,  while  other 


Snow  Crystals. 


crystals  are  shaped  like  those  shown  in  Figure  97.  Some 
of  the  most  beautiful  crystals  are  those  of  snow,  made 
by  the  freezing  of  moisture.  The  different  flakes  have 
varied  patterns,  but  they  all  have  six  sides  or  points 
(Figure  98). 


WATER  105 

Substances  which  do  not  crystallize  are  called  amor- 
phous, or  without  form. 

Evaporation.. —  Water  will  evaporate  even  when  the 
temperature  is  far  below  the  boiling  point.  Even  a 
cake  of  ice  will  decrease  in  size  through  evaporation 
without  melting.  Wet  clothes  hung  out  of  doors  on  a 
cold  day  will  often  remain  frozen  until  they  are  dry. 

The  rate  of  evaporation  depends  upon  the  following 
factors : 

1.  The  area  of  the  surface  exposed; 

2.  Temperature  of  the  liquid  ; 

3.  Pressure  of  the  atmosphere ; 

4.  Dampness  (humidity)  of  the  atmosphere  ; 

5.  Rate  of  renewal  of  fresh  air. 

Most  of  us  have  noticed  the  influence  of  some  of  these 
conditions.  1.  If  we  desire  to  evaporate  a  pint  of  water, 
we  can  do  so  more  quickly  if  we  put  the  water  in  a  shallow 
pan  than  if  we  put  it  into  a  deep  cup.  Evaporation  takes 
place  only  from  the  surface  of  liquids,  so  of  course  the 
greater  the  surface  exposed  the  faster  will  be  the  rate  of 
evaporation. 

2.  Evaporation  simply  means  that  some  of  the  mole- 
cules of  water  enter  the  air,  but  molecules  of  water  vapor 
in  the  air  also  reenter  the  water  in  the  exposed  vessel. 
Now  if  any  real  decrease  in  the  volume  of  the  water 
occurs,  it  must  mean  that  molecules  of  water  from  the 
vessel  enter  the  air  faster  than  those  in  the  air  enter  the 
water  in  the  vessel.     The  warmer  the  water  the  faster 
the  molecules  move  and  the  more  rapidly  they  pass  into 
the  air. 

3.  The  greater  the  pressure  of  the  atmosphere  the 
greater  will  be'  the  force  which  is  tending  to  prevent  the 
escape  of  the  little  molecules  of  water  from  its  surface 


106  GENERAL  SCIENCE 

into  the  air,  and  so  as  the  pressure  is  reduced  the  rising 
molecules  of  vapor  encounter  less  resistance  and  escape 
more  easily.  Sometimes  the  pressure  over  evaporating 
liquids  is  reduced  by  having  vacuum  pans,  which  are 
pans  with  air-tight  covers  connected  with  a  pump. 
When  air  is  partially  exhausted  from  these  pans,  evapora- 
tion is  greatly  hastened, 

4.  There  is  a  limit  to  the  amount  of  water  that  the  air 
can  hold ;   and  so,  if  the  atmosphere  is  already  saturated 
with  moisture  in  the  form  of  water  vapor,  no  more  evapo- 
ration can  take  place  from  the  liquids  under  it.     This 
simply  means  that  molecules  of  water  are  entering  the 
surface  of  the  liquid  from  the  air  as  fast  as  they  are  enter- 
ing the  air  from  the  liquid. 

5.  If  there  were  no  movement  of  air  over  an  evaporating 
liquid,  the  air  would  soon  become  saturated  with  water 
vapor  and  evaporation  would  cease.     The  oftener  the 
air  is  renewed  the  more  rapid  will  be  the  rate  of  evapora- 
tion. 

Some  liquids  evaporate  much  more  rapidly  than  others 
under  the  same  conditions.  Alcohol,  gasoline,  and  ether 
are  examples  of  such  liquids.  Liquids  which  evaporate 
rapidly  are  said  to  be  volatile,  while  others  like  heavy 
oils  are  said  to  be  non- volatile. 

Evaporation,  a  Cooling  Process.  —  Place  a  little  alcohol 
on  the  back  of  the  hand  and  blow  on  it.  Fasten  some 
cotton  around  the  bulb  of  a  thermometer,  noting  the 
temperature.  Now  wet  the  cotton  with  ether  and  take 
the  reading  of  the  thermometer  again.  What  is  the 
effect  in  each  of  these  cases? 

Evaporation  is  a  cooling  process,  because  heat  is  used 
in  the  change.  Evaporation  involves  a  change  of  state, 
and  energy  in  the  form  of  heat  is  necessary  for  such  a 


WATER  107 

change.  As  the  heat  is  used,  of  course,  the  temperature 
must  fall  in  those  objects  from  which  the  heat  was  ab- 
stracted. 

QUESTIONS 

1.  Why  will  clothes  dry  better  on  a  windy  day  than  on  a  still 
one? 

2.  Why  are  large  shallow  pans  used  in  making  maple  sirup? 

3.  What  is  the  temperature  of  deep  water?     Does  it  change 
much  in  summer  and  winter? 

4.  If  ice  is  0.92  as  heavy  as  water,  what  fractional  part  of  the 
ice  will  float  out  of  water? 

5.  Is  the  freezing  of  water  a  physical  or  chemical  change? 

6.  Why  is  it  difficult  to  cook  vegetables  at  Quito  ? 

7.  Why  are  vessels  often  broken  by  freezing  water? 

8.  If  ice  were  heavier  than  water,  would  there  be  any  disastrous 
results? 

9.  What   are   the   essential   differences   between   oxygen   and 
hydrogen  ? 

10.  Name  three  chemical  changes.     Six  physical  changes. 

11.  When  a  pan  is  over  a  gas  stove  with  the  flame  burning  low, 
water  forms  on  the  surface  of  the  pan  next  the  flame.     Why? 

12.  Can  you  see  steam?     What  is  it  we  see  and  call  steam? 

13.  Is  the  ocean  water  more  dense  than  the  water  of    Lake 
Erie?     Why? 

14.  When  we  heat  copper  sul-phate  crystals,  we  may  hear  little 
cracking  sounds.    What  causes  these  sounds? 


CHAPTER  VII 
USES   OF  WATER 

WHEN  pure  water  is  cooled  to  0°  Centigrade,  or  32° 
Fahrenheit,  it  freezes,  and  ice  is  formed.  With  the 
present  stage  of  civilization,  ice,  which  was  once  a  luxury, 
has  become  almost  a  necessity.  Large  quantities  of  ice 
are  cut  from  our  lakes  and  ponds  and  stored  for  summer 
use,  but  much  larger  quantities  are  manufactured  in  our 
modern  ice  plants. 

The  artificial  ice  has  several  advantages :  it  is  usually 
purer  than  the  natural  ice ;  it  is  free  from  air  spaces  and 
melts  more  slowly ;  and  since  nearly  every  municipality 
has  its  own  ice  plant,  the  distribution  is  a  much  simpler 
problem  than  when  the  ice  must  be  shipped  in  carload 
lots  to  remote  inland  points. 

Manufacture  of  Ice.  —  In  nearly  all  of  the  modern  ice 
plants,  the  low  temperature  required  for  freezing  the 
water  is  produced  by  the  evaporation  of  liquid  ammonia. 
We  have  already  learned  that  evaporation  is  a  cooling 
process.  It  requires  heat  to  evaporate  liquids,  and  the 
heat  is  taken  from  the  surrounding  objects,  thus  reducing 
their  temperature.  The  cooling  resulting  from  evapora- 
tion will  be  in  proportion  to  the  rate  of  evaporation. 
The  evaporation  of  liquid  ammonia  is  very  rapid,  and  in 
the  ice  plant  sufficient  heat  is  used  in  the  change  to  cool 
the  surrounding  objects  to  a  temperature  below  the 
freezing  point  of  water.  At  ordinary  temperatures 
ammonia  is  a  gas.  The  temperature  above  which 

108 


USES   OF  WATER 


109 


ammonia  gas  cannot  be  liquefied  is,  130°  Centigrade  (the 
Critical  Temperature).  At  temperatures  below  this 
point  it  may  be  liquefied  by  subjecting  it  to  great  pres- 
sure. At  80°  Fahrenheit  a  pressure  of  155  pounds  per 
square  inch  will  produce  its  liquefaction. 

Figure  99  is  a  diagram  of  the  essentials  of  a  modern  ice 
plant. 

The  condensing  pump  forces  the  ammonia  gas  into  the 
condensing  pipes  at  a  pressure  of  155  pounds  to  the 


FIG.  99. —A  Modern  Ice  Plant. 

square  inch  of  surface.  The  heat  of  the  condensation  of 
ammonia  is  carried  off  by  the  cold  water  which  is  kept  in 
contact  with  the  condensing  coils.  From  the  condenser 
the  liquid  ammonia  is  allowed  to  pass  slowly  through  the 
expansion  valve  at  D  into  the  coils  of  the  evaporator  C 
from  which  the  evaporated  ammonia  is  pumped,  so  that 
the  pressure  in  the  evaporating  pipes  is  maintained  at 
about  the  pressure  of  two  atmospheres.  The  pump 
shown  in  the  diagram,  acts  both  as  a  compressor  for  the 
ammonia  in  the  condensing  coils  and  an  exhaust  for  the 


110 


GENERAL  SCIENCE 


gas  in  the  evaporating  pipes.  As  the  liquid  ammonia 
passes  through  the  valve  at  D,  it  evaporates  so  rapidly 
that  enough  heat  is  taken  from  the  surrounding  pipes 
and  brine  to  cool  them  below  the  freezing  point  of  water. 
This  brine  then  circulates  around  the  cans  containing  the 
water  to  be  frozen.  It  is  possible  to  use  the  same  am- 
monia gas  over  and  over  again. 

Cold  Storage.  —  The  same  kind  of  apparatus  is  now 
used  in  the  artificial  cooling  of  cold  storage  rooms,  except 
that  the  cooled  brine  is  forced  through  pipes  placed  in 
the  rooms  to  be  cooled.  It  is  possible  with  such  a  system 
to  have  the  temperature  ranging  from  16°  Fahrenheit  up. 
Occurrence  of  Water.  —  Water  is  one  of  the  most 
widely  distributed  compounds.  It  occurs  in  all  three 
states  of  matter  and  is  very  useful  in  each  of  these  states. 
Besides  covering  three  quarters  of  the  earth's  surface, 
water  composes  a  large  part  of  the  earth  and  the  plants 
and  animals  that  live  on  it.  Our  own  bodies  are  70  per 

cent  water,  and  the 
foods  which  we  eat 
are  largely  composed 
of  it. 

Water  Pressure.  - 
We  are  all  aware  of 
the  pressure  that  is 
exerted  by  water.  If 
a  cork  is  held  under 
water  and  then  re- 
leased, it  will  rise  to 
the  surface.  This  is 
proof  of  the  upward 
It  is  this-  pressure  which  causes 


FIG.  100.  —  The  pressure  in  liquids  varies 
with  the  depth. 


pressure  of  the  liquid, 
boats  to  float. 


USES  OF  WATER 


111 


Experiment  30.  —  A  very  simple  experiment  may  be  arranged 
to  determine  whether  the  pressure  changes  as  the  depth  of  the 
water  is  increased.  Stretch  a  rubber  diaphragm  over  the  mouth 
of  a  thistle  tube  and  attach  the  tube  to  a  pressure  gauge  (Figure 
100).  The  working  of  the  apparatus  may  be  tested  by  pressing  on 
the  diaphragm  with  the  finger.  The  drop  of  ink  moves  out  as  the 
pressure  is  increased  and  returns  to  its  former  position  when  the 
finger  is  removed.  Test  the  pressure  at  different  depths  and  also 
at  the  same  depth  with  the  tube  in  a  number  of  different  positions. 
What  is  the  effect  of  doubling  the  depth?  Trebling  the  depth? 
What  is  the  effect  of  changing  the  direction  of  the  pressure  with 
the  depth  remaining  the  same? 

The  upward  force  on  any  horizontal  surface  in  a  liquid 
is  equal  to  the  weight  of  a  column  of  the  liquid  whose 
base  is  the  given 
surface  beneath 
the  free  surface 
of  the  liquid  and 
whose  height  is 
equal  to  the  depth 
of  the  liquid. 

Since  the  above   FIG.   101.  —  Irregular  Shapad  Vessels  having  Equal 
,    .  Bases. 

statement  is  true 

and  since  of  course  the  downward  force  on  such  a  surface 
is  exactly  equal  to  the  upward  force,  it  will  be  seen  that 
these  forces  are  not  dependent  on  the  shape  of  the  vessel 
but  simply  upon  the  area  of  the  surface  considered  and 
the  depth  and  density  of  the  liquid.  For  example,  if  the 
four  vessels  of  Figure  101  have  bases  of  the  same  area  and 
are  filled  with  the  same  liquid  to  the  same  depths,  the 
downward  pressure  on  the  bases  will  be  exactly  the  same 
in  each  case.  This  conclusion  seems  unreasonable  at  first, 
since  it  means  that  the  pressure  in  some  cases  is  much 
more  than  the  total  weight  of  the  water  in  the  vessel; 


112  GENERAL  SCIENCE 

however;  it  can  be  proved  true.  To  calculate  the  pressure 
in  terms  of  some  unit  we  have  only  to  take  area  X 
depth  X  weight  of  unit  volume.  At  a  given  depth  a  liquid 
presses  in  every  direction  with  exactly  the  same  force. 

Pressure  on  the  Sides  of  a  Tank.  —  It  is  quite  easy  to 
calculate  the  pressure  on  the  side  of  a  tank,  since  the 
pressure  at  any  point  of  unit  area  is  equal  to  the  weight 
of  the  column  of  water  which  has  for  its  area  this  same 
unit  and  for  its  height  the  depth  of  the  water.  Since  the 
pressure  increases  in  direct  proportion  to  the  depth  below 
the  free  surface  of  the  liquid,  the  total  pressure  on  the 
side  of  the  tank  will  be  found  by  multiplying  the  area  of 
the  side  of  the  tank  by  the  average  depth  of  all  the  units 
of  area  below  the  free  surface  of  the  liquid  (area  X  aver- 
age depth  X  weight  of  unit  volume).  The  pressure 
against  one  square  centimeter  of  the  wall  of  a  tank  con- 
taining water,  with  the  upper  edge  of  the  square  centi- 
meter 10  centimeters  below  the  surface  of  the  water,  will 
be  IX  10. 5X1  gram.  What  will  be  the  pressure  if 
inches  and  pounds  be  substituted  for  centimeters  and 

grams  ? 

1  cubic  foot  of  water  weighs  62.5  pounds 
1  cubic  centimeter  of  water  weighs  1  gram 

Transmission  of  Pressure  by  Liquids.  —  We  have 
learned  that  pressure  in  a  free  liquid  depends  simply 
upon  the  depth  and  density  of  the  liquid.  From  this 
Pascal  (1623-1662),  a  French  scientist  and  philosopher, 
deduced  a  very  surprising  and  important  conclusion  which 
is  now  known  as  Pascal's  Law. 

In  the  city  water  system  the  pressure  in  one  part  of 
the  system  is  transmitted  to  all  parts  of  the  city.  This 
pressure  is  often  obtained  by  means  of  a  reservoir  located 
on  some  high  spot  of  land  and  into  which  the  water  is 


USES  OF  WATER  113 

pumped.  The  pressure  may  be  obtained,  however, 
directly  from  the  pumps.  In  either  case  it  is  often  trans- 
mitted through  miles  of  underground  pipes  to  thousands 


FIG.  102.  —  High  Pressure  Fire  Service  Streams. 

The  four  pumps  are  discharging  12,000  gallons  per  minute.     The  streams 
are  600  feet  long. 

of  faucets.  The  fire  protection  of  a  large  number  of  our 
cities  is  dependent  upon  the  water  pressure  of  such  a 
system  (Figure  102). 

Pascal  discovered  that  pressure  applied  anywhere  to  a 
body  of  confined  liquid  is  transmitted  by  the  liquid  so  as 
to  act  with  undiminished  force  on  every  unit 
of  area  of  the  containing  vessel. 

Suppose  a  vessel  such  as  shown  in  Figure  103 
to  be  filled  with  water  to  the  level  ab.  Suppose 
the  area  of  the  upper  part  of  the  vessel  is  one 
square  inch.  Now  if  an  ounce  of  water  be  poured 
into  the  tube,  an  extra  ounce  of  pressure  will  FIG.  103. 


114 


GENERAL  SCIENCE 


be  added  to  every  square  inch  of  surface  in  the  vessel. 
If  the  inside  area  of  the  vessel  be  16  square  inches,,  the 
extra  force  exerted  will  be  one  pound. 

The  Hydraulic  Press.  —  It  is  obvious  that  a  piston 
may  be  used  instead  of  water  in  the  above  illustration , 


FIG.  104.  —  Hydraulic  Press. 

and  this  means  is  commonly  used  to  secure  the  applica- 
tion of  great  pressure  at  a  given  place.  Such  a  machine 
is  called  the  hydraulic  press.  This  machine  consists  of 
two  communicating  cylinders  each  fitted  with  a  piston. 
One  cylinder  is  usually  much  larger  than  the  other  (Figure 
104).  If  the  areas  of  the  pistons  are  in  the  ratio  of  one 


U.  S.  Geological  Survey. 
An  Artesian  Well  at  Woonsocket,  South  Dakota.     The  Jet  is  97  feet  high. 


USES  OF  WATER  115 

hundred  to  one,  according  to  Pascal's  Law  a  pressure  of 
one  pound  on  the  smaller  piston  will  transmit  a  force  of 
one  hundred  pounds  to  the  larger  piston.  By  increasing 
the  ratio  of  the  larger  piston  to  the  smaller  piston,  we 
can  obtain  enormous  pressures.  Hydraulic  presses  are 
used  in  many  places  where  a  great  force  is  needed ;  as  in 
lifting  jacks,  cotton  presses,  iron  testing  machines,  and 
many  others. 

It  will  be  observed  that  while  the  hydraulic  press  exerts 
a  very  great  force  it  acts  quite  slowly  through  a  given 
space.  For  example,  if  the  ratio  of  the  areas  of  the  pistons 
is  100  to  1  and  the  smaller  piston  mpves  one  inch,  the 
larger  piston  will  move  but  TSTF  of  an  inch,  so  that  the 
products  of  the  force  times  the  distance  which  the  re- 
spective pistons  move  are  always  equal. 

Artesian  Wells  are  dependent  on  the  principle  of  trans- 
mission of  pressure  by  liquids.  Water  percolates  through 


FIG.  105.  —  Artesian  Basin,  Showing  Arrangement  of  Rock  Strata. 

the  soil  and  finally  becomes  entrapped  under  an  imper- 
vious stratum  of  rock  through  which  it  finds  no  outlet. 
If  a  well  is  bored  through  this  stratum,  water  gushes  up 
often  to  a  considerable  height.  Figure  105  shows  a  dia- 
gram of  what  the  geologists  call  an  artesian  basin.  Water 
enters  the  stratum  A  at  the  outcropping  ends.  The  im- 
pervious strata  hold  it  entrapped  until  a  boring  is  made. 
Probably  the  most  famous  well  is  at  Grenelle  near  Paris. 
It  is  1740  feet  deep  and  delivers  over  500  gallons  of  water 
a  minute  at  a  temperature  of  84°  Fahrenheit.  The 


116  GENERAL  SCIENCE 

deepest  artesian  well  is  near  Berlin.  It  is  4200  feet  deep. 
Near  Kissengen,  Germany,  is  an  artesian  well  which  is 
1800  feet  deep  and  throws  a  stream  of  water  58  feet  high. 
A  large  number  of  artesian  wells  exist  in  the  United 
States. 

QUESTIONS 

1.  Calculate  the  pressure  on  an  area  2  centimeters  square  on 
the  side  of  a  vessel,  the  top  of  the  area  being  12  inches  below  the 
surface  of  the  water  in  the  vessel. 

2.  Find  the  force  in  pounds  acting  on  the  bottom  of  a  box  10 
inches  long,  4  inches  wide,  and  5  inches  deep,  filled  with  water. 

.  3.  A  vessel  in  the  shape  of  a  cone  is  10  inches  high  and  has  a 
base  of  12  square  inches.  What  is  the  pressure  on  the  base  when 
filled  with  water? 

4.  In  the  above  is  the  pressure  on  the  base  greater  than  the 
force  required  to  lift  the  cone?     Why? 

5.  In  the  second  problem  what  would  be  the  pressure  if  alcohol 
were  used  instead  of  water,  considering  alcohol  to  be  .8  as"  heavy 
as  water? 

6.  If  the  large  piston  of  a  hydraulic  press  has  a  diameter  of  20 
inches  and  the  smaller   piston  a  diameter  of'l  inch,  what  force 
will  be  exerted   by  the  large  piston  when  a  force  of   5  pounds  is 
applied  to  the  small  piston? 

7.  Why  is  artificial  ice  ordinarily  purer  than  natural  ice? 

Archimedes'  Principle.  —  Archimedes,  a  great  scientist 
and  mathematician  who  lived  in  Syracuse,  Sicily  (287-212 
B.C.),  was  the  first  person  to  announce  the  discovery  that 
a  floating  body  displaces  its  own  weight  of  the  fluid  and 
that  a  body  immersed  in  a  fluid  is  buoyed  up  with  a  force 
equal  to  the  weight  of  the  liquid  displaced. 

The  story  is  told  that  Hiero,  the  tyrant  of  Syracuse, 
suspecting  that  the  crown  that  he  had  had  made  was  not 
pure  gold  as  specified,  ordered  Archimedes  to  discover 
whether  or  not  this  were  true.  It  was  a  great  problem 
for  Archimedes  to  find  a  way  to  do  this  without  destroy- 


USES  OF  WATER  117 

ing  the  crown.  While  in  his  bath  one  day,  he  happened 
to  notice  the  loss  of  weight  of  his  own  body,  and  the  whole 
principle  suddenly  occurred  to  him  that  a  body  immersed 
in  water  must  lose  a  weight  equal  to  the  weight  of-  the 
water  displaced.  This  discovery  made  his  problem  quite 
simple,  since  gold  has  a  volume  which  in  proportion  to  its 
weight  is  smaller  than  that  of  any  other  metal  except 
platinum.  Archimedes  determined,  therefore,  that  the 
crown  was  made  of  pure  gold,  since  an  equal  volume  of 
any  other  metal  would  lose  a  greater  proportion  of  its 
weight  when  immersed  in  water. 

Most  of  us  are  acquainted  with  this  principle  long 
before  any  statement  of  it  is  made.  We  know  that  many 
objects  float,  and  it  is  quite  evident  that  if  an  object  such 
as  a  piece  of  wood  or  a  boat  floats,  the  upward  force  of 
the  water  must  be  equal  to  the  weight  of  the  body.  A 
piece  of  iron  will  sink  in  water,  but  if  mercury  is  used,  the 
iron  will  float  as  cork  on  water.  An  iron  vessel  will  float 
on  water  because  the  vessel  is  so  shaped  that  it  displaces 
more  water  than  the  volume  of  the  metal  used  in  its  con- 
struction. As  a  vessel  is  loaded,  it  sinks  deeper  and 
deeper  into  the  water,  but  only  sinks  deep  enough  to  dis- 
place an  amount  of  water,  equal  in  weight  to  the  weight 
of  the  ship  and  its  cargo. 

Submarines. — A  submarine  boat  is  so  constructed  that 
no  water  can  enter  it  even  if  it  is  completely  submerged, 
excepting  as  permitted  to  enter  by  the  occupants  of  the 
boat.  If  the  boat  is  to  dive,  water  is  admitted  into 
special  compartments  until  the  weight  of  the  boat  slightly 
exceeds  the  weight  of  the  water  it  displaces.  If  the  weight 
of  the  boat  exactly  equals  the  weight  of  the  water  it  dis- 
places, it  will  remain  stationary  at  any  depth  below  the 
surface.  When  the  boat  is  to  rise  to  the  surface,  water 


118  GENERAL  SCIENCE 

*, 
is  forced  out  of  the  special  compartments  and  air  takes  its 

place,  making  the  boat  lighter. 

Density  of  a  Solid  Heavier  than  Water.  —  It  is  quite 
easy  to  find  the  density  of  a  regular-shaped  solid  by 
measurement,  the  density  of  a  body  being  its  mass 
divided  by  its  volume.  With  irregular  solids,  however, 
other  means  must  be  employed ;  since,  while  it  is  always 
possible  to  find  the  mass  of  a  body  by  weighing,  it  is  some- 
times quite  difficult  to  find  the  volume  of  it  by  measur- 
ing. Archimedes'  principle,  however,  furnishes  an  easy 
and  accurate  method  for  determining  the  volume  of  any 
solid,  regular  or  irregular.  Water  has  unit  density,  since 
a  cubic  centimeter  of  water  weighs  a  gram.  Now  since  a 
solid  immersed  in  water  is  buoyed  up  with  a  force  equal 
to  the  weight  of  the  water  it  displaces,  the  loss  in  weight 
of  the  solid  when  weighed  in  water  will  just  equal  the 
weight  of  an  equal  volume  of  water. 

The  statement,  the  density   =  ma.ss — ,  becomes  numer- 

volume 

ically   the   same    as     density  =  mass      —    — . 

loss  of  weight  in  water. 

Density  of  Solids  Lighter  than  Water.  —  The  density  of 
solids  lighter  than  water  may  be  found  in  a  similar  way  by 
using  a  heavy  sinker  to  hold  the  lighter  solid  under  water. 
Arrange  the  apparatus  as  shown  in  Figure  106.  Find  the 
weight  with  the  body  in  the  air  and  the  sinker  in  water, 
then  weigh  both  under  water.  The  difference  in  the  two 
weights  will  be  the  buoyant  force  on  the  body  alone  and 
will  be  equal  to  the  weight  of  the  displaced  water  and 
numerically  equal  to  the  volume  of  the  body.  The  density 
may  then  be  obtained  by  the  use  of  the  same  equation  : 
mass 


density 


volume  or  loss  of  weight  in  water. 


USES   OF  WATER 


119 


The  density  of  liquids  may  be  found  by  a  comparison 
of  the  weights  of  equal  volumes  of  water  and  the  liquid 
whose  density  is  to  be  determined.  Special  bottles,  com- 
mercially called  "Specific  Gravity"  bottles,  are  used  for 


FIG.  106.  —  Apparatus  for  Determining  the  Density  of  Insoluble  Substances 
Which  are  Lighter  than  Water. 

this  purpose.     After  the  bottle  has  been  dried,  weigh  it 
filled  with   the  liquid  whose   density  is   undetermined. 
The  density  of  several  liquids  should  be  determined. 
See  table  of  densities  on  page  36. 

QUESTIONS 

1.  Which  is  denser,  cream  or  milk? 

2.  Will  gold  float  or  sink  in  mercury? 

3.  Why  is  it  easier  to  swim  in  the  water  of  the  ocean  than  in 
the  water  of  Lake  Erie? 

4.  As  a  vessel   passes  from  the  river  into  the  ocean,  will  its 
water  line  rise  or  fall? 


120.      ,  GENERAL  SCIENCE 

5.  A  block  of   wood  8  inches  high   sinks  4  inches  in  water. 
What  is  the  density  of  the  wood? 

6.  Suppose  the  above  block  of  wood  sinks  5  inches  in  alcohol, 
what  is  the  density  of  the  alcohol? 

7.  A  stone  weighs,  15  pounds  in  air  and  10  pounds  in  water. 
What  is  the  density  of  the  stone? 

8.  Why  does  a  stone  seem  lighter  under  water? 

9.  Explain  the  principle  of  the  hydraulic  press. 

10.  Would  a  piece  of  iron  float  in  melted  copper? 

11.  What  solids  sink  in  mercury? 

12.  A  solid  weighs  25  grams  in  air  and  20  grams  in  water. 
What  does  an  equal  volume  of  water  weigh?     What  is  the  density 
of  the  solid? 

13.  How  much  water  does  a  floating  piece  of  wood  displace? 

14.  An  iron  weight  weighs  10  pounds  in  air  and  140  ounces  in 
water.     What  is  its  density? 

15.  A  fresh  egg  sinks  in  pure  water.     Why  ?    Why  does  it  not 
sink  in  strong  brine?     How  can  you  find  the  density  of  an  egg? 

16.  How  may  you  determine  the  density  of  a  piece  of  butter? 

17.  How  could  Archimedes  tell  whether  or  not  Hiero's  crown  was 
pure  gold? 

Common  Uses  of  Water.  —  Great  quantities  of  water 
are  used  daily  in  our  large  cities,  and  the  problem  of 
supplying  pure  and  wholesome  water  for  the  people  of  a 
great  city  like  New  York  is  by  no  means  a  small  one. 
Each  city  has  a  different  problem,  depending  upon  its 
location,  the  nature  of  the  underlying  soil  and  rock,  and 
the  amount  of  water  needed.  Many  cities  pump  the 
water  from  deep  wells  near  by ;  others  carry  the  water  in 
immense  tubes  for  miles  from  some  source  which  has  a 
higher  altitude  than  the  city  to  be  supplied ;  other  cities 
like  Chicago  or  Cleveland  take  the  water  from  the  lakes 
near  by;  still  others  use  the  rivers  (Figure  107). 

Hardness  of  Water.  —  Water  is  usually  spoken  of  as 
hard  or  soft.  Hardness  of  water  may  be  measured  by  its 
soap-consuming  power.  The  hardness  of  water  depends 


USES  OF  WATER 


121 


upon  the  amount  of  mineral  matter  that  it  has  dissolved 
from  the  ground  that  it  has  passed  through.  Usually 
this  mineral  matter  is  calcium  carbonate  (lime)  and 
magnesium  carbonate,  but  often- other  minerals  are  found. 
The  ocean  is  said  to  contain  traces  of  all  the  soluble  ele- 
ments, together  with  large  quantities  of  the  substances 
we  have  named  above,  and  common  salt.  Well  water  is 
always  hard,  but  of  varying  degrees  of  hardness.  The 


FIG.  107.  —  Low  Lift  Pump  Room,  Cleveland,  Ohio. 
This  is  the  largest  low  lift  pumping  station  in  the  United  States. 

water  of  the  streams  is  usually  quite  soft,  increasing  in 
hardness  as  it  gets  farther  away  from  its  source  and 
comes  in  contact  with  more  soil  from  which  it  dissolves 
small  quantities  of  solid  matter.  If  hard  water  is  boiled 
for  a  short  time,  a  white  deposit  will  be  noticed  in  the 
vessel  in  which  it  was  boiled.  This  deposit  is  mostly  lime. 
Is  there  any  deposit  when  soft  water  is  boiled  ? 

Spring  water  is  simply  rain  water  that  has  percolated 


122  GENERAL  SCIENCE 

through  the  soil.  In  doing  so  the  water  takes  into  solu- 
tion various  salts.  Sometimes  these  salts  have  certain 
medicinal  properties,  and  the  water  containing  them  is 
sold  for  medicinal  purposes.  There  now  exist  a  number 
of  health  resorts  which  base  their  claims  on  the  peculiar 
properties  of  the  water  of  their  springs. 

Purification  of  Water.  —  In  many  cities  the  water  is  so 
impure  that  some  means  must  be  taken  to  free  it  from 
impurities.  Some  cities  have  established  immense  filtra- 
tion plants  to  remove  the  solid  matter  from  the  water 
supply.  Columbus,  Ohio,  has  such  a  plant  which  has 
been  in  successful  operation  for  a  number  of  years,  with 
excellent  results  from  both  the  standpoint  of  health  and 
of  suitability  for  commercial  uses.  In  this  plant  much 
of  the  lime  in  solution  is  removed  by  the  use  of  chemicals. 
Ordinarily  a  city  filtration  plant  consists  simply  of  large 
areas  of  sand,  gravel,  and  sometimes  charcoal  through 
which  the  water  is  allowed  to  percolate.  After  one  filter 
has  been  used  for  a  while  the  water  is  turned  into  another 
filter  to  permit  the  first  to  be  purified  by  the  action  of  the 
air  and  sun.  Such  filters  remove  most  organic  matter, 
but  of  course  they  do  riot  remove  the  soluble  substances. 

A  filter  of  sand  and  charcoal  may  be  used  for  remov- 
ing the  solid  particles  from  water,  and  such  filters  are 
quite  common  both  on  a  small  and  large  scale.  However, 
such  filters  soon  become  clogged  with  small  particles  of 
clay  and  other  foreign  substances  and  must  be  renewed 
if  their  efficiency  is  to  be  maintained. 

To  separate  all  the  solid  matter  in  the  form  of  solutions 
from  water,  distillation  must  be  resorted  to.  This  is 
merely  a  process  of  driving  the  water  off  in  steam  and 
catching  and  condensing  the  steam  again.  For  home  use 
the  water  may  be  rendered  safe  by  boiling,  since  all 


USES  OF  WATER 


123 


dangerous  disease  germs  are  killed  by  the  continuous 
application  of  heat.  To  kill  the  germ  of  typhoid  fever, 
water  should  be  boiled  at  least  twenty  minutes.  It  is 
usually  quite  easy  to  take  this  precaution  when  the 
purity  of  the  water  is  in  question,  and  by  doing  so  manv 
lives  may  be  saved. 

City  Water   Supply.  —  Civilization  requires  an  abun- 
dance of  water.     A  water  famine  is  more  serious  than  a 


FIG.  108.  — A  Steel  Intake  Crib  about  Five  Miles  from  Shore. 

food  famine.  The  community  utilizes  water  for  the  re- 
moval of  sewage  and  for  fire  protection.  The  various 
manufacturing  plants  use  vast  quantities  of  water,  and 
in  the  homes  it  is  a  constant  necessity  for  drinking  pur- 
poses, for  cooking,  for  the  cleansing  of  soiled  clothes  and 
dishes,  and  for  bathing. 

The  water  supply  of  any  city  always  furnishes  a  real 
community  problem.  The  Romans  brought  water  from 
the  Apennine  Mountains  to  Rome  in  great  aqueducts. 
The  cities  on  the  Great  Lakes  obtain  their  water  supply 
from  the  lakes,  but  it  is  necessary  to  take  the  water  from 
" cribs"  considerable  distances  from  the  shore  to  avoid 
the  impurities  from  the  sewage  which  is  poured  into  the 


124 


GENERAL  SCIENCE 


lake  (Figure  108).  Chicago  no  longer  pours  its  sewage 
into  Lake  Michigan  but  into  the  Mississippi  River  by 
way  of  the  Chicago  "  Drainage  Canal "  and  the  Illinois 
River.  'Many  small  inland  cities  rely  upon  large  wells 
for  their  water  supply,  while  the  large  inland  cities  take 


FIG.  109.  —  Pure  Water  may  be  Obtained  by  Distillation. 

the  water  from  near-by  streams.  Such  water  is  usually 
quite  impure  and  should  be  filtered  and  in  many  cases 
boiled  before  it  is  used  for  drinking  purposes. 

Experiment  31.  —  Arrange  a  Liebig  condenser  as  shown  in 
Figure  109.  Fill  the  flask  with  water  that  has  been  discolored  with 
foreign  matter,  such  as  coal  dust,  dirt,  or  ink.  As  the  water 
passes  into  steam  and  is  again  condensed  it  will  be  found  to  be  as 


FIG.  110.  —  Home  Made  Condenser. 

clear  as  water  can  be.  This  water  is  also  free  from  solid  matter. 
In  the  absence  of  a  Liebig  condenser  a  condenser  may  be  made  by 
arranging  a  large  glass  tube  as  shown  in  Figure  110. 


USES   OF    WATER  125 

QUESTIONS 

1.  What  is  the  source  of  the  water  supply  of  your  city? 

2.  Has  there  ever  been  an  epidemic  of  typhoid  fever  in  your 
city?     If  so,  what  was  the  cause? 

3.  Is  any  method  to  purify  the  water  supply  used  in  your  city? 

4.  Should  rain  water  be  used  for  drinking  purposes?     Why? 

5.  Where  do  the  five  largest  cities  of  the  United  States  get 
their  water  supply? 

6.  What  does  the  term  "  plumbing  "  include? 

7.  What  is  the  use  of  "  traps  "  in  plumbing  systems? 

8.  Why  does  the  water  pressure  vary  at  different  points  in  a 
city  water  system? 


CHAPTER  VIII 
HEAT 

HEAT  is  a  form  of  energy  with  which  we  are  well  ac- 
quainted, since  there  are  so  many  effects  of  heat  that  are 
very  important  in  our  daily  lives.  Heat  was  supposed 
to  be  a  fluid  until  the  beginning  of  the  nineteenth  century. 
This  fluid  was  called  "  caloric  "  and  its  mysterious  passage 
from  one  body  to  another  was  supposed  to  result  in 
changes  of  temperature. 

Heat  results  from  the  motion  of  molecules.  As  we  have 
learned,  matter  is  made  up  of  minute  particles  which, 
although  closely  crowded  together,  still  have  spaces 
between  them.  These  particles  are  in  constant  motion,' 
striking  each  other  at  every  turn.  The  velocity  with 
which  these  little  particles  move  to  and  fro  in  their  short 
excursions  determines  the  temperature  of  the  body  - 
the  faster  the  motion  the  higher  the  temperature.  When 
the  activity  of  the  particles  is  lessened,  the  body  becomes 
cooler.  If  the  vibrations  are  sufficiently  rapid,  both  heat 
and  light  are  produced. 

Sources  of  Heat.  -  -  There  are  a  number  of  sources  of 
heat,  but  the  principal  sources  are  friction,  compression, 
chemical  action,  the  sun,  body  heat,  and  electrical  resist- 
ance. 

Friction.  —  The  resistance  offered  by  the  sliding  of  one 
body  on  another  is  friction,  and  it  is  a  well-known  fact 
that  friction  produces  heat.  Most  of  us  have  observed 
this  in  numerous  instances.  The  journals  of  cars  sometimes 

126 


HEAT  127 

become  so  hot  that  the  packing  in  the  boxing  becomes 
ignited.  In  machinery,  oil  is  used  in  many  places  to 
reduce  the  friction  and  prevent  excessive  heating. 

When  a  bullet  is  stopped  by  a  steel  plate,  it  becomes 
hot.  The  motion  has  been  changed  to  another  form  of 
energy,  namely,  heat.  It  is  the  same  with  friction. 
Friction  retards  the  motion,  and  this  loss  in  motion  shows 
up  as  heat.  The  greater  the  loss  in  motion  or  the  greater 
the  friction,  the  greater  the  amount  of  heat  developed.  It 
is  said  that  man  formerly  obtained  his  fire  by  rubbing 
two  sticks  together.  We  still  obtain  our  fire  by  friction, 
but  the  process  has  been  very  much  simplified  by  the 
substitution  of  other  substances  for  one  of  the  sticks,  as 
in  the  modern  match. 

Compression.  —  In  the  chapter  which  treated  of  the 
making  of  artificial  ice  it  was  noted  that  the  expanding 
ammonia  gas  produced  a  temperature  .cold  enough  to 
freeze  water.  If  the  gas  is  compressed,  an  opposite  ef- 
fect is  produced,  the  gas  becoming  much  warmer.  This 
may  be  tested  with  a  common  bicycle  pump  by  closing  the 
tube  leading  from  the  pump  and  repeatedly  compressing 
the  air.  Note  the  temperature  of  the  barrel  of  the  pump. 

Chemical  Action.  —  For  many  years  man  has  used  fire, 
and  in  so  doing  he  uses  some  of  the  energy  that  has  been 
stored  up  by  the  plants.  The  chief  fuels  are  wood,  coal, 
natural  gas,  petroleum,  and  alcohol.  When  man  causes 
these  fuels  to  unite  with  oxygen  and  burn,  he  is  using  some 
of  the  energy  of  the  sun  which  was  stored  up  by  the  plants, 
and  in  some  cases  by  the  animals. 

Sun.  —  Practically  all  the  heat  of  the  earth's  surface 
comes  from  the  sun.  When  we  realize  that  we  receive 
only  one  two-billionth  of  the  sun's  heat  and  still  have 
enough  to  make  the  earth  a  very  pleasant  place  in  which 


128 


GENERAL  SCIENCE 


to  live,  we  can  get  some  vague  idea  of  the  very  great 
amount  of  heat  in  the  sun. 

Measurement  of  Temperature.  —  While  we  have  no 
difficulty  in  deciding  whether  we  are  too  warm  or  too  cold, 
we  cannot  rely  on  our  sense  of  feeling  to  determine  tem- 
perature except  within  a  very  narrow  range  ;  and  then  the 
result  is  only  a  comparative  one.  For  example,  it  is  a 
well-known  fact  that  if  a  person  puts  one  hand  into  hot 
water  and  the  other  into  cold  water  for  a  time,  and  then 
puts  both  hands  into  warm  water  it  will  feel  cold  to  the 
hand  which  has  been  in  hot  water,  and  hot  to  the  hand 


100°  C 


ing  Wafer 


FIG.   111.  —  Determination  of  the  Fixed  Points  on  a  Thermometer. 

which  has  been  in  cold  water.  By  comparison  the  sensa- 
tions are  correct,  but  as  a  test  of  temperature  they  are 
quite  unreliable.  The  instrument  used  for  measuring 
temperatures  is  called  a  thermometer.  The  ordinary 
commercial  thermometer  consists  of  a  capillary  tube 
with  a  bulb  at  the  end.  The  tube  is  partly  filled  with 
mercury,  and  after  the  air  from  the  remaining  part  has 
been  removed  the  tube  is  sealed  at  the  top. 

The  freezing  and  boiling  points  of  water  enable  us  to 
graduate  the  thermometer  easily.  The  sealed  tube  is 
placed  in  melting  ice,  and  the  point  at  which  the  mercury 


HEAT 


129 


212° 


stands  is  marked  as  the  freezing  point.  This  point  is  called 
zero  on  the  Centigrade  scale  and  thirty-two  degrees  on 
the  Fahrenheit  scale  (Figure  111).  To  locate  the  boiling 
point  of  water,  place  the  tube  in  boiling  water,  or  better, 
the  steam  immediately  over  boiling 
water.  The  point  at  which  the  mer- 
cury now  stands  is  marked  100  on  the 
Centigrade  scale  and  212  on  the  Fah- 
renheit. The  space  between  these  two 
fixed  points  is  divided  into  one  hun- 
dred equal  parts  for  the  Centigrade 
thermometer  and  180  equal  parts  for 
the  Fahrenheit  scale.  In  scientific 
work  the  Centigrade  scale  has  come 
into  almost  universal  use  and  in  many 
countries  it  is  the  only  thermometer 
used.  It  is  unfortunate  that  the 
Fahrenheit  thermometer  ever  came 
into  use  in  our  country  as  a  weather 
bureau  instrument,  since  its  scale  is  so 
cumbersome.  It  must  be  remembered 
that  the  two  thermometers  differ  only 
in  their  scales  (Figure  112). 

The  difference  between  the  freez- 
ing point  and  the  boiling   point   on 
the  Centigrade  scale  is  100  degrees  and  on  the  Fahrenheit 
scale  180  degrees. 

180°  F.  equal  100°  C. 

18°  F.  equal    10°  C. 

1°  F.  equal      f  °  C. 

or         1°  C.  equal      f°  F. 

Were  it  not  for  the  fact  that  the  freezing  point  is  marked 
32  on  the  Fahrenheit  scale,  it  would  only  be  necessary 


inn* 

IUU 

P" 

-17° 

}  A 

r 

-40° 

) 

-40° 


FIG.  1 12.  —  Compari- 
son of  the  Fahrenheit 
and  Centigrade  Ther- 
mometer Scales. 


130  GENERAL  SCIENCE 

to  multiply  by  one  or  the  other  of  the  above  factors  in 
changing  from  one  reading  to  the  other.  As  it  is,  to  change 
degrees  Centigrade  to  degrees  Fahrenheit  multiply  by  1 
and  add  32. 

C  X  *  +  32  =  F 

To  change  degrees  Fahrenheit  to  degrees  Centigrade, 
subtract  32  from  the  number  of  degrees  and  multiply  by  f . 

*  (F  -  32)  =  C 

Mercury  is  quite  generally  used  in  ordinary  ther- 
mometers, but  since  mercury  freezes  at  about  -  40°  Centi- 
grade and  boils  at  about  350°  Centigrade,  mercury 
thermometers  cannot  be  used  for  extreme  temperatures. 
Alcohol  thermometers  are  commonly  used  in  cold  cli- 
mates. For  temperatures  above  the  boiling  point  of  mer- 
cury, other  kinds  of  thermometers  are  used. 

EXERCISES 

1.  Reduce  60°  F.  to  Centigrade  degrees. 

2.  Reduce  -  20°  F.  to  Centigrade  reading. 

3.  Reduce  -  40°  C.  to  Fahrenheit. 

4.  Mercury  boils  at  350°  C.     What  will  this  temperature  be  in 
Fahrenheit  scale? 

5.  Absolute  zero  is  —  273°  C.     Reduce  this  to  Fahrenheit. 

Effects  of  Heat.  —  The  three  main  physical  effects  of 
heat  are  expansion,  fusion,  and  vaporization.  There  are 
other  effects,  but  they  are  mainly  physiological  and  chem- 
ical effects. 

Expansion.  —  The  first  effect  of  heat  on  a  body  is  to 
cause  its  molecules  to  move  faster.  As  they  move  faster 
all  the  molecules  strike  against  their  neighbors  with  greater 
force,  pushing  them  farther  and  farther  apart.  This 


HEAT 


131 


causes  the  body  as  a  whole  to  become  larger,  or  we  say 
expansion  has  taken  place. 

Many  materials  expand  irregularly  when  heated,  but 
rubber  is  the  only  material  which  contracts  when  heated. 

Experiment  32.  —  The  ball  and  ring  ex- 
periment is  a  classical  one  (Figure  113).  Given 
an  iron  ring  and  an  iron  ball  that  will  just  pass 
through  it  at  ordinary  temperature.  Heat  the 
ball  and  see  if  it  will  now  pass  through  the 
ring.  In  what  direction  has  the  ball  ex- 
panded? Now  heat  the  ring  and  see  if  the 
ball  will  pass  through.  Cubical  expansion  is 
expansion  in  every  direction.  Linear  expan- 
sion means  simply  an  increase  in  length. 

Experiment  33.  —  Arrange  an  iron  rod  as 
shown  in  Figure  114  so  that  one  end  rests  on 
an  ordinary  knitting  needle  attached  to  a 
pointer.  As  the  rod  is  heated  it  increases  in  length.  This  expan- 
sion is  shown  by  the  movement  of  the  pointer. 


FIG.  113.  — The  Ball 
and  Ring  Experiment. 


FIG.    114.  —  Expansion  of  Solids. 
As  the  rod  expands  or  contracts  the  pointer  moves  correspondingly. 

Expansion  of  Liquids.  —  Liquids  expand  as  we  have 
already  seen  in  the  mercury  and  alcohol  thermometers. 

Experiment  34.  — Take  a  flask  and  fit  it  with  a  two-hole  rubber 
stopper.  Pass  a  glass  tube  about  sixteen  inches  long  through  one 
hole  of  the  stopper  and  a  thermometer  through  the  other  hole. 
Fill  the  flask  with  water  and  place  the  stopper  in  the  flask  so  that  the 
water  rises  a  fraction  of  an  inch  above  the  base  of  the  stopper. 
Now  heat  the  water  slowly,  noting  temperatures  and  heights  of  the 
water  in  the  tube.  A  scale  may  be  improvised  from  an  ordinary 
meter  bar  as  shown  in  Figure  115.  Draw  a  curve  of  the  expan- 


132 


GENERAL  SCIENCE 


sion  of  water,  plotting  scale  readings  on  the  horizontal  axis  and 
thermometer  readings  on  the  vertical  axis. 

We  have  already  spoken  of  the 
great  importance  of  the  irregular 
expansion  of  water.  Review  it 
here. 

Expansion  of  Gases.  —  Gases  are 
no  exception  to  the  rule  that  heat 
expands  matter.  The  effect  of  heat 
on  gases  is  very  marked.  Since  the 
molecules  are  farther  separated  in 
gases  than  in  other  forms  of  matter, 
the  application  of  heat  greatly  in- 
creases their  speed  and  their  ex- 
pansive force. 

Experiment  35.  — Fit  a  Florence  flask 

with  a  one-hole  rubber  stopper  and   a 

glass  tube  twenty  inches  long    (Figure 

116).     Invert  this  apparatus  in  a  vessel 

of  water  and   apply  heat  to  the  flask. 

What  happens?     Allow  the  flask  to  cool.     Why  does  the  water 

ascend  ?     How  could  the  amount  of  expansion  of  the  air  in  the  flask 

be  determined  ? 

If  several  gases 
are  tested,  it  will 
be  found  that  they 
expand  about  the 
same  amount  for 
each  degree  of 
temperature  and 
not  irregularly  as 
do  solids  and 
liquids.  A  gas  ex- 

FIG.  116. —  Expansion  of  Gases.  pands     2T3"    °f    ^S 


FIG.  115. —  Expansion  of 
Liquids. 


HEAT  133 

volume  at  zero  for  each  degree  Centigrade  of  rise  in  tem- 
perature. This  number  is  called  the  coefficient  of  expan- 
sion of  gases.  If  a  gas  is  cooled  from  zero,  it  contracts 
at  the  same  rate ;  however,  before  it  reaches  —  273°  it 
becomes  a  liquid  and  so  no  longer  obeys  the  law  stated 
above.  All  gases  have  been  liquefied  by  low  temperature 
and  great  pressure. 

Fusion.  —  Changing  a  body  from  a  solid  to  a  liquid 
form  is  called  fusion.  Other  terms  which  have  the  same 
meaning  are  liquefaction  and  melting.  The  reverse 
process  is  called  freezing  or  solidification.  It  is  a  well- 
known  fact  that  the  melting  point  of  ice  and  the  freezing 
point  of  pure  water  is  the  same,  32°  F.  or  0°  C.  Other 
substances  have  different  melting  points,  but  in  every  case 
the  melting  point  and  the  solidifying  point  of  a  substance 
is  the  same. 

Table  of  Melting  Points 

Alcohol -  130.5°     Lead 326° 

Mercury -  39         Zinc 433 

Ice .     .         0         Silver 950 

Lard 33         Copper 1100 

Paraffin 54          Cast  iron 1200 

Sulphur 115         Platinum 1775 

Tin   .     ....     .;    .     .     .  232          Iridium 1950 

Experiment  36.  —  Place  some  pieces  of  ice  in  a  beaker  and  heat 
slowly  over  a  small  flame.  Stir  the  ice  and  water  constantly  with 
a  thermometer  and  note  the  temperature  from  time  to  time. 

Most  liquids  decrease  in  volume  when  they  solidify, 
but  the  opposite  is  true  of  water,  liquid  iron,  and  a  few 
other  substances  in  which  there  is  a  sudden  marked  in- 
crease in  volume  at  the  moment  of  solidification.  Water 
increases  about  nine  per  cent  on  freezing,  and  the  force 
exerted  is  great  enough  to  burst  the  usual  containers  such 
as  water  pipes  and  pitchers  and  other  household  utensils. 


134  GENERAL  SCIENCE 

Experiment  37.  —  Fill  an  ordinary  large-mouthed  bottle  with 
water  and  fit  it  with  a  one-hole  rubber  stopper.  Insert  a  glass  tube 
in  the  stopper  and  crowd  the  stopper  down  until  the  water  fills  the 
tube.  Now  place  the  bottle  in  a  freezing  mixture  of  ice  and  salt 
and  watch  the  contraction  and  expansion  of  the  water.  What  is 
the  first  change  noticed?  At  what  temperature  does  water  cease 
to  contract  and  begin  to  expand  ?  Watch  the  experiment  until  the 
whole  mass  of  water  in  the  bottle  is  frozen. 

Vaporization.  -  -  The  changing  of  a  liquid  to  a  gas  is 
called  vaporization.  Slow  vaporization  is  called  evapora- 
tion. It  takes  place  at  all  temperatures  below  the  boiling 
point.  Ebullition  or  boiling  takes  place  at  a  definite  tem- 
perature, and  if  the  pressure  on  the  liquid  does  not  change, 
the  temperature  will  remain  constant  until  the  liquid 
is  completely  vaporized. 

Boiling.  —  While  evaporation  takes  place  only  at  the 
surface  of  the  liquid,  boiling  takes  place  throughout  the 
entire  mass.  It  is  interesting  to  watch  the  water  in  a 
beaker  as  it  approaches  the  boiling  point.  From  where 
do  the  air  bubbles  come  that  gather  on  the  walls  of  the 
beaker?  Do  the  first  bubbles  of  steam  get  smaller  or 
larger  as  they  rise  in  the  liquid?  What  causes  the  agi- 
tation of  the  liquid?  What  becomes  of  the  water  that 
disappears?  If  a  thermometer  is  placed  in  the  liquid  it 
will  probably  read  less  than  100°.  Why? 

Determine  the  boiling  point  of  alcohol. 

Boiling  Points  at  Standard  Pressure 

Ether       .     .     .     ...     .     .".  38°  Water       ...     .     .     .  100° 

Chloroform  .......  60  Mercury  .......  350 

Alcohol 78  Sulphur 440 

Benzine   ........  80  Zinc 1050 

Relation  of  Boiling  Point  to  Pressure.  —  Of  course  the 
atmosphere  is  exerting  a  pressure  on  the  surface  of  a 


HEAT 


135 


liquid  at  all  times.     The  boiling  point  of  a  liquid  is  the 
temperature  at  which  the  vapor  pressure  of  the  liquid 

becomes  greater 
than  the  atmos- 
pheric pressure  on 
the  liquid.  Since 
the  atmospheric 
pressure  becomes 
less  and  less  as  we 
ascend,  the  boiling 
point  for  any  cer- 
tain liquid  will  be 
lowered  as  we  as- 
Water boils 


FIG.    117.  —  Boiling   Water    at    a   Temperature 
below  100°  Centigrade  by  Reducing  the  Air  Pres-    Cend. 


sure  with  the  Aid  of  an  Air  Pump. 


at 


temperature  on  the  tops  of  our  high  mountains  than  at 
sea  level. 

Experiment  38.  —  Boil  some  water  in  a  flask  and  then  remove  it 
from  the  fire  and  place  it  under  the  receiver  of  an  air  pump  (Figure 
117).  Exhaust  some 
of  the  air  and  note 
the  result.  How  do 
you  explain  the  fact 
that  the  water  again 
,begins  to  boil  vio- 
lently when  it  is  evi- 
dently much  colder 
than  when  it  was  boil- 
ing over  the  fire? 

Experiment  39.  - 
Fill  a  Florence  flask 
half  full  of  water  and 
boil  the  water  vigor- 
ously   for    a    minute.   FlG-  us.  —  Boiling  Water  at  a  Temperature  below 
Now    close    the   flask  100°  Centigrade. 


136  GENERAL  SCIENCE 

with  a  rubber  stopper  and  invert  it  on  a  ring  stand  (Figure  118)  and 
pour  cold  water  over  it.  The  water  in  the  flask  will  boil  vigor- 
ously. When  the  boiling  point  is  reduced  as  low  as  possible,  remove 
the  stopper  and  take  the  temperature.  Why  do  we  need  to  boil 
the  water  some  time  before  starting  the  experiment?  Why  is  it 
difficult  to  cook  eggs  or  potatoes  by  boiling  on  high  mountains  ? 

Laws  of  Ebullition. 

1.  Under  constant  pressure  every  liquid  has  a  definite 
boiling  point. 

2.  While  the  liquid  is  boiling  the  temperature  remains 
constant  until  all  is  vaporized. 

3.  The   boiling   point   varies   with   the   pressure,   the 
greater  the  pressure  the  higher  the  boiling  point  and  vice 
versa. 

EXERCISES  AND  QUESTIONS 

1.  Why  do  telegraph  wires  sag  more  in  summer  than  in  winter  ? 

2.  What  temperature  Fahrenheit  is  equal  to  35°  Centigrade? 

3.  A  rod  40  inches  long  expands  A  of  an  inch  when  heated  50°. 
How  much  would  it  expand  if  heated  1°? 

4.  Why  are  railroad  tracks  not  laid  so  that  the  ends  meet  when 
laid  in  winter? 

5.  How  could  you  make  an  air  thermometer? 

6.  To  what  temperature  must  a  quart  of  air  at  0°  C.  be  heated 
to  double  its  volume  ? 

7.  Why  does  freezing  often  burst  water  pipes? 

8.  Will  roads  dry  faster  on  a  still  or  windy  day? 

9.  Why  does  sweet  oil  evaporate  so  slowly? 

10.  How  do  salts  in  solution  affect  the  boiling  point  of  water? 
Test. 

11.  How  may  we  separate  alcohol  and  water? 


CHAPTER   IX 
QUANTITY    OF    HEAT    AND    TRANSMISSION    OF    HEAT 

TEMPERATURE  and  quantity  of  heat  must  not  be  con- 
sidered the  same  thing.  Temperature  or  degree  of  heat 
indicates  how  hot  or  cold  a  body  is,  and  depends  upon  the 
rapidity  with  which  the  molecules  are  moving  and  not 
upon  the  number  of  molecules.  Heat,  or  quantity  of 
heat,  which  a  body  possesses  depends  upon  the  speed  of 
the  molecules,  the  number  of  molecules  affected,  and  also 
upon  the  kind  of  molecules  of  which  a  body  is  composed. 

The  Calorie.  --  The  metric  unit  used  in  measuring  the 
quantity  of  heat  in  a  body  is  called  the  calorie.  It  is  the 
amount  of  heat  required  to  warm  one  gram  of  water 
through  one  degree  Centigrade.  It  is  also  the  amount  of 
heat  given  off  by  one  gram  of  water  when  its  temperature 
falls  one  degree  Centigrade.  To  warm  one  gram  of  water 
from  0°  C.  to  100°  C.  requires  one  hundred  calories.  The 
same  amount  of  heat  is  required  to  heat  four  grams  of 
water  from  0°  C.  to  25°  C.,  or  ten  grams  of  water  from 
0°  C.  to  10°  C. 

Heat  Capacity.  —  Different  substances  have  different 
capacities  for  taking  heat.  If  equal  amounts  of  water 
and  mercury  be  subjected  to  the  same  heat,  the  mercury 
will  become  hot  much  quicker  than  the  water.  The 
quantity  of  heat  that  is  required  to  raise  the  temperature 
of  a  gram  of  water  from  0°  C.  to  1°  C.  will  raise  the  tem- 
perature of  thirty  grams  of  mercury  from  0°  C.  to  1°  C. ; 
or  it  requires  thirty  times  as  much  heat  to  raise  a  given 

137 


138  GENERAL  SCIENCE 

mass  of  water  through  a  number  of  degrees  as  to  raise 
the  same  mass  of  mercury  the  same  number  of  degrees. 
Water  has  a  greater  capacity  for  heat  than  mercury. 
The  ratio  of  the  heat  capacity  of  any  substance  to  the  heat 
capacity  of  water  is  called  its  specific  heat.  For  example, 
the  specific  heat  of  iron  is  about  £,  or  in  other  words  a 
pound  of  water  in  cooling  from  100°  to  0°  will  give  out  as 
much  heat  as  a  pound  of  iron  in  cooling  from  900°  to  0°. 

Experiment  40.  —  In  one  beaker  put  200  grams  of  water  at  15° 
and  in  another  beaker  put  200  grams  of  water  at  35°.  Now  pour 
the  two  together  and  take  the  temperature.  What  temperature 
would  you  expect  ?  Substitute  200  grams  of  lead  shot  for  the  water 
in  the  second  beaker  and  repeat  the  experiment. 

Table  of  Specific  Heats 

Water 1.000  Copper 095 

Alcohol 610  Silver 057 

Ice 504  Tin .     .     .056 

Aluminum 218  Mercury 033 

Iron    .     .     .-.     .     .     .     .       .113  Lead       32 

Latent  Heat.  —  It  was  noticed  that  when  heat  was 
continuously  applied  to  a  mixture  of  melting  ice  and  water 
the  temperature  did  not  change  but  remained  near  0° 
until  all  the  ice  was  melted.  What  becomes  of  the  heat? 
Evidently  it  represents  the  work  which  has  been  done  in 
effecting  the  change  of  state  from  a  solid  to  a  liquid. 
Eighty  calories  of  heat  are  required  to  change  a  gram  of 
ice  at  0°  to  water  at  the  same  temperature.  Thus  water 
is  said  to  have  a  latent  heat  of  eighty  calories.  Since  this 
heat  disappears  .when  ice  or  other  substances  melt  and 
reappears  when  they  solidify,  it  has  been  called  latent  or 
hidden  heat.  Although  the  name  is  not  appropriate  it  is 
the  one  which  is  commonly  used.  Heat  of  fusion  is  a 
better  name. 


QUANTITY  AND  TRANSMISSION  OF  HEAT        139 

To  change  a  gram  of  water  at  100°  to  steam  at  the  same 
temperature  requires  536  calories  of  heat,  steam  being  said 
to  have  a  heat  of  vaporization  of  536. 

Experiment  41.  —  Place  200  grams  of  finely  cracked  ice  in  a  tin 
cup.  Upon  this  pour  200  grams  of  water  at  80°  and  note  the  result- 
ing temperature.  Why  is  the  resulting  temperature  not  40°? 

Experiment  42.  — Pass  steam  through  a  steam  trap  (Figure  119) 
into  a  vessel  containing  300  grams  of  water  at  about  15°?  Take 


FIG.  119.  —  A  Steam  Trap. 

the  temperature  of  the  water  and  then  weigh  carefully.     From  the 
data  calculate  the  heat  of  vaporization. 
300  (t  -  15) 

W  -  300 
t  =  final  temperature,  w  =  final  weight,  H  =  heat  of  vaporization. 

The  condensation  of  steam  is  a  great  source  of  heat  and 
is  much  used  in  systems  of  heating  for  buildings.  The 
condensation  point  is  the  point  at  which  the  most  heat 
is  given  off.  For  example,  a  gram  of  water  gives  up  536 
calories  of  heat  in  simply  changing  from  steam  at  100° 
to  water  at  100°. 

We  are  now  better  able  to  understand  why  evaporation 
is  a  cooling  process.  It  is  simply  that,  since  only  the 


140 


GENERAL  SCIENCE 


molecules  which  move  very  rapidly  are  able  to  get  away 
from  the  surface  of  the  liquid,  it  is  the  slow-moving  mole- 
cules that  are  left.  Temperature  depends  upon  the 
speed  of  the  molecules  in  a  body.  If  the  swiftly  moving 
molecules  are  removed,  the  temperature  falls. 

Transference  of  Heat.  —  Iron  is  a  better  conductor  of 
heat  than  glass.  In  fact  all  metallic  solids  are  better  con- 
ductors of  heat  than  non-metallic  solids  such  as  glass  and 
wood. 

Experiment  43.  —  Hold  a  glass  rod  and  an  iron  rod  so  that  the 
end  of  each  rod  will  be  in  the  flame.  The  other  end  of  the  metal 
rod  soon  becomes  hot,  while  with  the  glass  rod  no  change  is  observed. 

Some  Common  Substances  Arranged  in  the  Order  of  their 
Relative  Heat  Conductivities 


Silver     ........  100 

Copper 74 

Gold 53. 

Brass 25 

Zinc  .     .     .     , 19 

Tin    .  15 


Iron  .  .  . 
Lead  .  .  . 
German  silver 
Ice  .  .  . 
Glass  .  .  . 
Hard  rubber 


12 

8.5 

6.2 
.21 
.05 
.025 


Experiment  44.  —  Arrange  four  wires,  one  of  copper,  one  of 
brass,  one  of  iron,  and  one  of  German  silver,  on  a  piece  of  cardboard 
as  shown  in  Figure  120.  Hold  the  ends  in  the  flame  of  a  Bunsen 

burner.  Determine  their  relative 
conductivities  by  touching  a  match 
to  them  at  equal  distances  from 
the  flame. 

Liquids  and  gases  are  poor 
conductors  of  heat.  That 
water  is  a  poor  conductor 
may  be  shown  in  the  follow- 
ing way  :  Weight  a  small  piece 
of  ice  so  that  it  will  rest  at 

120.  —  Metals    vary    m    their 

conduction  of  heat.  the  bottom  OI  a  test  tUD6  full 


FIG. 


QUANTITY  AND  TRANSMISSION  OF  HEAT        141 


*  * 


of  cold  water.  Heat  the  upper  part  of  the  tube  with  a 
Bunsen  burner  as  shown  in  Figure  121.  The  water  at 

the  upper  part  of  the  tube 
may  be  boiled  for  some  time 
without  melting  the  ice. 

Experiment  45.  —  Place  the  bulb 
of  an  air  thermometer  a  fraction 
of  an  inch  below  the  surface  of  the 
water  in  a  funnel  arranged  as  in 
Figure  122.  Now  pour  some  ether 

FIG.  121.  -Water  is  a  poor  con-  on  the  water  and  Se1j  Jt  on  fire' 
ductor  of  heat,  as  is  shown  by  the  Hardly  any  change  in  tempera- 
exP3riment.  ture  win  be  indicated  by  the  air 

thermometer.  The  conductivity  of  water  is  about  'y*W  that  of 
silver. 

Gases  are  even  poorer  conductors  than  liquids.  Dry 
air  has  almost  no  conductivity.  The  warmth  of  fur 
and  woolen  garments  is  due  to 
the  fact  that  they  have  so  many 
minute  spaces  containing  non-con- 
ducting air.  There  are  many  uses 
of  non-conducting  air.  It  is  on 
account  of  this  that  snow  is  such 
an  efficient  protection  to  wheat  and 
other  vegetation.  Ice  houses  have 
double  walls  with  the  space  between 
filled  with  sawdust.  Many  houses 
now  have  double  windows.  Loosely 
woven  cloth  is  warmer  than  the  (  ^ 

same  weight  of  closely  woven  ma- 

terial. Loose  and  fibrous  materials  are  always  poor  con- 
ductors on  account  of  the  air  entrapped  between  their 
fibers. 


142  GENERAL  SCIENCE 

Conductivity  of  the  Earth.  —  Although  the  interior  of 
the  earth  is  highly  heated,  the  surface  of  the  earth  is  very 
little  affected  by  it.  As  we  go  from  the  surface  toward  the 
center  of  the  earth  we  find  that  the  ground  is  quite  cold  for 
a  few  hundred  feet.  As  we  go  still  deeper  the  temperature 
increases  at  the  rate  of  about  1°  C.  for  every  110  feet  of 
descent. 

Water  pipes  and  drain  pipes  are  placed  a  few  feet  under 
ground  so  that  they  will  be  out  of  reach  of  the  frost. 

Conductivity  and  Sensation.  —  On  a  cold  day  metals 
feel  much  colder  than  a  piece  of  wood,  although  the  tem- 
perature of  the  wood  be  the  same  as  the  temperature  of  the 
metal.  On  the  other  hand,  if  both  bodies  have  been  lying 
in  the  hot  sun  the  metal  will  seem  much  hotter  to  the  hand 
than  the  wood.  The  explanation  is  found  in  the  fact 
that  the  metal,  being  a  much  better  conductor  of  heat  than 
wood,  conveys  the  heat  away  from  the  hand  much  more 
rapidly  when  it  is  cold,  and  conveys  the  heat  to  the  hand 
much  more  rapidly  when  it  is  hot,  than  does  the  wood. 
If  the  metal  is  warmer  than  the  body,  it  will  feel  hotter 
than  the  wood ;  if  it  is  colder  than  the  body,  it  will  feel 
colder  than  the  wood.  We  speak  of  "  warm  blankets, " 
when  the  blankets  are  evidently  no  warmer  than  the 
surrounding  objects.  We  simply  mean  that  the  blankets 
are  poor  conductors  of  heat,  and  so  they  feel  warmer  than 
the  other  objects.  So  also  the  rug  feels  much  warmer  than 
a  tiled  floor  or  an  oilcloth. 

The  Fireless  Cooker.  —  This  is  merely  an  arrangement 
of  non-conducting  substances  to  prevent  the  escape  of 
heat  from  heated  foods  placed  in  it  (Figure  123).  The  two 
walls  of  the  fireless  cooker  are  separated  by  a  thick  layer 
of  non-conducting  materials  such  as  sawdust,  felt,  or  cork 
shavings.  These  inclose  a  considerable  amount  of  air, 


QUANTITY  AND   TRANSMISSION   OF  HEAT        143 


which  is  a  very  poor  conductor  of  heat.     The  packing 
prevents  convection  currents  and  retards  radiation  and 

conduction.  Food  to 
be  cooked  is  first 
heated  and  then 
placed  in  the  cooker 
where  the  cooking 
continues,  since  the 
heat  cannot  escape. 

It  is  quite  easy  for 
anyone  who  is  at  all 
handy  with  carpenter 
tools  to  make  a  very 
good  fireless  cooker 
after  the  plan  of  the 


Sawdust 


one  shown  in  the  cut. 
The  Thermos  Bot- 
tle. —  The     thermos 
It  is  made  of  two 


FIG.  123.  —  A  Homemade  Tireless  Cooker. 

bottle  is  similar  to  the  fireless  cooker, 
glass  bottles  which  are  sealed  together  at 
the  top  after  the  air  in  the  space  between 
them  has  been  exhausted.  This  prevents 
the  loss  of  heat  from  the  inside  bottle  by 
convection  and  conduction.  The  outside 
bottle  is  lined  on  the  inside  with  an  excel- 
lent reflecting  surface  which  prevents  a 
loss  of  heat  from  the  inside  bottle  by 
radiation  (Figure  124). 

The  Davy  Safety  Lamp.  —  If  a  piece 
of  wire  gauze  be  held  above  an  open  gas 
jet  and  a  match  applied  below  the  gauze, 
the  flame  will  burn  below  the  gauze  as  „  FlG-  12,4-~Cross 

'  Section  of  Thermos 

in  ligure  125  (o),  but  it  will  not  pass  Bottle. 


144  GENERAL  SCIENCE 

through  to  the  upper  side.  If  it  is  ignited  above  the 
gauze,  the  flame  will  burn  as  shown  in  Figure  125  (a),  but 
it  will  not  pass  through  to  the  lower  side. 

The  metal  gauze  conducts  the  heat  away  from  the  flame 
so  rapidly  that  the  gas  on  the  other  side  is  not  heated  to  the 
ignition  point.  It  is  on 
this  principle  that  the 
Davy  Safety  Lamp,  much 
used  in  mines,  depends. 
The  distinctive  feature  of 
the  lamp  is  that  the  flame 
is  completely  inclosed  by 

a  Wire  gauze   Chimney,   SO    FIG.   125.  —  Effect  of   Wire  Gauze  on  a 

that  if  the  mine  is  full  of 

inflammable   gases,  they  are  not   ignited  by  the  lamp 

burning  inside  the  gauze. 

Convection  in  Liquids.  —  Although   liquids   are   poor 

conductors  of  heat,  they  may  be  readily  heated  by  con- 
vection. In  conduction  there  was  no  move- 
ment of  the  molecules  from  one  end  of  the 
metal  rod  to  the  other,  but  only  vibrations 
of  the  molecules  in  a  limited  space.  In 
convection,  however,  the  molecules  move 
from  place  to  place.  If  the  heat  had  been 
applied  to  the  bottom  of  the  test  tube  in 
Figure  121,  the  ice  would  have  melted 
quickly,  and  the  whole  tube  of  water  would 
FIG.  126.—  The  have  heated  evenly.  This  shows  that  heat 


water    is^eveniy  is  transferred  much  more  rapidly  from  the 


heated      because  bottom  of  the  tube  toward  the  top  than 

of  the   convection 

currents.  from  the  top  toward  the  bottom. 

Experiment  46.  —  Fill  a  Florence  flask  two  thirds  full  of  water 
and  drop  into  it  a  crystal  of  potassium  permanganate.     Heat  the 


QUANTITY  AND  TRANSMISSION  OF  HEAT        145 

bottom  of  the  flask  with  the  tip  of  a  Bunsen  burner  flame.  The 
coloring  matter  will  show  the  direction  of  the  convection  currents 
(Figure  126).  The  water  nearest  the  flame  becomes  heated  and 
expands,  thus  becoming  less  dense  than  the  surrounding  water. 
This  lighter  water  is  then  forced  up  by  the  denser  water  which  comes 
in  from  the  sides  to  take  its  place. 

Convection  in  Gases.  —  The  winds  are  convection 
currents  in  the  atmosphere  caused  by  the  unequal  heating 
of  the  earth  by  the  sun.  This  principle  easily  explains  the 
land  and  sea  breezes  near  the  coasts  of  large  bodies  of 
water.  During  the  daytime  the  land  is  heated  more 
rapidly  than  the  water,  the  specific  heat  of  water  being 
much  greater  than  that  of  the  earth.  The  hot  air  over 
the  land,  being  lighter,  is  forced  up  by  the  cooler  air  from 
the  ocean.  This  is  the  sea  breeze  which  blows  during  the 
daytime  and  reaches  its  maximum  strength  usually  late 
in  the  afternoon.  At  night  the  earth  cools  more  rapidly 
than  the  sea,  and  in  a  short  time  the  sea  is  warmer  than 
the  land  and  the  current  of  air  is  reversed.  This  is  the 
land  breeze  which  blows  during  the  night  and  reaches  its 
maximum  toward  morning.  These  winds  are  more  notice- 
able in  the  tropics,  since  the  change  in  temperature  from 
day  to  night  is  greatest  there. 

Radiation.  —  When  we  stand  before  a  fireplace,  it  is 
evident  that  we  are  receiving  heat  that  comes  to  us 
neither  by  conduction  nor  convection.  It  cannot  be  due 
to  conduction,  because  the  conductivity  of  air  is  very 
small.  It  cannot  be  due  to  convection,  because  the  cur- 
rents of  air  are  moving  toward  the  fire  instead  of  away 
from  it.  There  must  therefore  be  some  way  in  which  heat 
travels  across  space  other  than  by  conduction  or  con- 
vection. This  third  method  of  heat  transference  in  which 
the  heat  emanates  in  straight  lines  from  a  source  inde- 


146  GENERAL  SCIENCE 

pendently  of  air  currents  or  any  conducting  matter  is 
called  radiation. 

It  will  be  well  for  us  to  note  some  of  the  differences 
between  conduction,  convection,  and  radiation. 

Conduction  and  convection  are  comparatively  slow, 
while  radiation  is  rapid.  The  sun's  heat  comes  to  us 
with  the  enormous  speed  of  light,  186,000  miles  a  second. 
The  heat  which  comes  to  us  by  radiation  comes  in  straight 
lines,  while  conducted  or  convected  heat  may  come  by  the 
most  roundabout  paths.  A  screen  placed  between  the 
source  of  radiant  heat  and  a  body  will  cut  off  the  heat  from 
the  body. 

Radiant  heat  will  pass  through  certain  media  without 
heating  them.  The  heat  from  the  sun  will  pass  through 
ordinary  window  glass  and  leave  it  much  colder  than  the 
objects  it  falls  upon  inside  the  room.  Also  the  upper 
regions  of  the  atmosphere  are  very  cold  even  in  the  hottest 
time  of  the  year. 

QUESTIONS  AND  PROBLEMS 

1.  Tubs  of  water  are  sometimes  put  in  cellars  in  cold  weather 
that  the  freezing  of  the  water  may  prevent  the  freezing  of  the  vege- 
tables.    Explain  this  phenomenon. 

2.  Why  is  a  quart  of  heated  water  a  better  foot-warmer  than  an 
equal  volume  of  heated  lead  ? 

3.  How  did  "  latent  heat  "  get  its  name? 

4.  100  grams  of  water  at  10°  C.  are  mixed  with  200  grams  of 
water  at  50°  C.     What  is  the  resulting  temperature? 

5.  If  20  grams  of  ice  at  0°  are  mixed  with  100  grams  of  water  at 
80°  what  will  be  the  temperature? 

6.  Why  do  we  put  salt  on  ice  in  an  ice-cream  freezer? 

7.  What  is  the  temperature  of  a  mixture  of  ice  and  water? 

8.  What  must  be  the  temperature  of  the  water  if  when  equal 
weights  of  water  and  ice  at  0°  are  mixed  the  result  is  water  at  0°  ? 

9.  Water  boils  at  90°  C.  at  Quito.     How  do  you  account  for 
the  low  boiling  point? 


QUANTITY  AND  TRANSMISSION  OF  HEAT        147 


10.  Why  do  small  bubbles  rise  in  a  vessel  of  water  that  is  being 
heated  long  before  the  boiling  point  is  reached? 

11.  Why  is  scalding  by  steam  more  serious  than  scalding  by 
water  at  the  same  temperature? 

12.  How  do  freezing  and  thawing  break  up  rocks? 

13.  If  10  grams  of  steam  at  100°  are  mixed  with  80  grams  of 
water  at  0°,  what  will  be  the  resulting  temperature  ? 

14.  Why  are  stove  irons  commonly  made  with  wooden  handles  ? 

15.  Why  do  we  wrap  ice  in  blankets  to  keep  it  from  melting? 

16.  Why  is  woolen  cloth  warmer  than  linen? 

17.  How  may  we  prove  that  air  goes  up  over  a  hot  stove? 

18.  What  is  the  principle  involved  in  the  fireless  cooker? 

19.  Why  is  the  air  inside  a  hothouse  warmer  than  the  air  out- 
side, even  if  it  is  not  heated  artificially? 

20.  How  may  we  prove  that  radiant  heat  and  light  travel  at 
the  same  speed? 

2 1 .  Why  is  there  no  loss  of  heat  by  convection  in  a  thermos  bottle? 

Heating  and  Ventilating  of  Buildings.  —  All  three  modes 
of  heat  transference  are  used  in  the  heating  and  ventilating 
of  our  homes  and  other 
buildings,  but  convection 
is  by  far  the  most  impor- 
tant principle  involved. 
Hot-air  and  hot-water 
systems  are  both  appli- 
cations of  this  principle. 

Hot-air  Heating. — This 
system  is  in  quite  com- 
mon use  in  small  build- 
ings. It  consists  of  a 
furnace  which  heats  the 
air  in  a  chamber  (Figure 
127)  surrounding  the  fire 
box.  As  the  air  is  heated,  convection  currents  are 
produced  in  the  pipes  leading  to  the  different  rooms 


FIG.  127. 
Diagram  of  a  Hot-air  Heating  System. 


148  GENERAL  SCIENCE 

of  the  house.  After  losing  some  of  its  heat  the  air 
returns  to  the  furnace  through  the  cold-air  duct,  where 
it  is  mixed  with  fresh  air  from  the  outside  and  re- 
heated. Many  furnaces  have  no  fresh-air  inlet.  The 
air  in  houses  having  this  sort  of  furnace  is  almost 
certain  to  have  many  impurities  in  it,  since 
the  only  sources  of  fresh  air  are  the  cracks 
around  the  doors  and  windows.  The  air 
which  feeds  the  fire  does  not  reach  the 
rooms,  but  passes  out  the  chimney,  as 
indicated  by  the  arrows.  After  the  fire  is 
well  started  the  damper  should  be  closed, 
since  a  great  deal  of  heat  is  lost  by  way 
of  the  chimney. 

Hot- water  Heating.  —  Figure  128  shows 
an  arrangement  which  illustrates  the  prin- 
ciple of   hot-water  heating.      The  whole 
FiG.i28~—  Con-   apparatus  is  filled  with  water,  the  water 
vection  Currents  in   ^  ^  Upper  vessel  being  colored.     When 

£L  JulQUlQ* 

heat  is  applied  to  the  lower  vessel,  con- 
vection currents  will  be  produced,  as  indicated  by  the 
arrows. 

There  are  several  different  ways  of  arranging  hot-water 
systems.  One  arrangement  is  shown  in  Figure  129.  The 
water  is  heated  in  the  jacket  around  the  furnace  A  and 
rises  to  the  reservoir  R,  returning  through  pipes  pp'  by 
way  of  the  radiators  BBf.  The  circulation  in  this  system 
is  maintained  in  the  same  way  as  in  the  apparatus  shown 
in  Figure  128. 

In  modern  buildings  a  system  known  as  the  "  direct- 
indirect  "  is  now  much  used.  In  this  system  fresh-air 
ducts  lead  to  coils  heated  by  steam  or  hot  water.  These 
coils  heat  the  air,  which  by  convection  is  carried  to  the 


QUANTITY  AND  TRANSMISSION  OF  HEAT        149 

• 

different  rooms.  In  large  systems  fans  are  used  to 
supplement  the  convection  currents,  thus  insuring  a  more 
even  distribution  of  heat  in  the  building. 

The  Thermostat.  —  The  thermostat  is  an  instrument 
used  to  regulate  the  temperature  of  rooms  arid  buildings. 
Figure  130  shows  the  working  principle  of  a  simple  form  of 
thermostat.  The  vertical  bar  is  a  part  of  two  electric 


FIG.  129.  —  Hot-wat2r  System  for  House  Heating. 

circuits.  The  uneven  expansion  and  contraction  of  the 
two  elements  of  the  compound  bar  throws  the  vertical 
rod  against  A  when  the  room  becomes  too  hot  and  against 
B  when  it  becomes  too  cold.  Electromagnets  in  the  two 
circuits  control  the  supply  of  steam,  hot  water,  or  hot  air 
to  the  different  rooms  and  thus  regulate  the  temperature. 
Ventilation.  —  Since  the  lungs  are  constantly  exchang- 
ing large  quantities  of  air  laden  with  carbon  dioxide  for 
oxygen,  it  is  necessary  that  the  air  in  the  rooms  in  which 


150 


GENERAL  SCIENCE 


B 


we  live  be  renewed  frequently.  All  modern  schoolrooms 
and  public  halls  are  now  provided  with  systems  of  ventila- 
tion or  apparatus  to  force  in  fresh  air 
and  remove  foul  air.  The  basis  of  all 
ventilation  methods  is  found  in  the  fact 
that  cold  air  is  heavier  than  warm  air. 
The  air  in  a  room  is  usually  colder  near 
the  floor  than  near  the  ceiling. 

If  a  house  is  heated  by  stoves  or 
fireplaces,  no  special  provision  for  ven- 
tilation is  necessary;  but  where  other 
systems  6f  heating  are  used,  some  at- 
tention should  be  paid  to  the  question 
of  proper  ventilation.  A  simple  experi- 
ment may  be  performed  to  illustrate  the 
way  in  which  convection  operates  to 
ventilate  our  houses. 


Iron. 


FIG.  130.  —  Ther- 
mostat whose '  Action 
Depends  upon  . the 
Unequal  Expansion 

Place  a  lighted  of  Two  Metals- 
candle  in  a  shallow  vessel  containing  a- little  water.  Now 
bring  a  tall  lamp  chimney  down  over  it  (Figure  131). 
The  flame  will  slowly  die  down  and  finally  go 
out.  Why?  If  the  chimney  is  raised  a  slight 
distance  above  the  water,  the  dying  flame  will 
brighten  at  once.  Why?  If  a  thin  metal  or 
cardboard  partition  is  lowered  in  the  chimney 
almost  to  the  flame,  the  latter  will  burn  con- 
tinuously although  the  bottom  of  the  chimney 
be  under  water.  The  reason  will  be  evident 
if  a  piece  of  burning  torch  paper  is  held  near 
the  chimney. 

In  order  to  secure  satisfactory  ventilation 
it  is  estimated  that  a  room  should  be  supplied 
with  a  minimum  of  thirty  cubic  feet  of  fresh  air  per  minute 
for  each  person.  If  the  speed  at  which  the  fans  drive 


FIG.  131. 


QUANTITY  AND  TRANSMISSION  OF  HEAT        151 

the  air  in  a  school  building  is  three  hundred  feet  a 
minute,  the  area  of  the  opening  required  for  each  person 
is  about  fifteen  square  inches. 

Need  of  Moisture  in  the  Air.  —  It  is .  quite  important 
that  the  air  in  our  homes,  schoolrooms,  and  other  such 
buildings  have  the  proper  amount  of  moisture  in  it; 
When  the  humidity  of  the  air  is  less  than  40,  it  takes 
up  the  perspiration  from  our  bodies  too  rapidly,  and  the 
skin  becomes  dry.  When  the  humidity  is  more  than  60, 
the  perspiration  does  not  evaporate  rapidly  enough,  and 
the  air  seems  oppressive  or  "  muggy. " 

As  cold  air  enters  a  heating  system  and  is  heated,  its 
capacity  for  holding  moisture  is  greatly  increased,  while 
the  amount  of  moisture  in  it  has  not  been  changed.  As 
a  result  the  amount  of  moisture  present  in  the  air  of  our 
homes  is  usually  too  small. 

In  hot-air  furnaces  care  should  be  taken  to  keep  the 
water  pan  in  the  air  box  full  of  water.  If  other  systems 
of  heating  are  used,  water  should  be  kept  in  the  rooms  in 
open  dishes,  or  small  buckets  of  water  may  be  hung  on 
small  wires  in  the  registers. 

QUESTIONS 

1.  How  is  your  building  heated? 

2.  What  is  the  objection  to  forcing  air  into  a  room  faster  than 
350  feet  a  minute? 

3.  Explain   why   the   old-fashioned   fireplace    furnished    good 
ventilation. 

4.  Why  do  we  need  more  air  during  sleep? 

5.  How  are  most  ordinary  dwelling  houses  ventilated? 


CHAPTER  X 
WEATHER 

Meaning  of  Term  "  Weather."  —  The  term  "  weather  "  is 
a  comprehensive  one.  It  includes  all  the  many  conditions 
of  the  earth's  atmosphere,  such  as  its  temperature,  its 
pressure,  and  the  amount  of  moisture  it  contains,  the 
variations  of  the  wind,  the  amount  of  rainfall,  and  the 
appearance  of  the  sky.  We  have  made  quite  a  careful 
study  of  the  two  substances  with  which  we  are  concerned 
in.  the  study  of  weather.  These  two  substances  are  air 
and  water  —  air  or  atmosphere,  as  the  outer  portion  of 
the  earth ;  and  water  in  its  many  forms :  as  water  vapor 
in  the  atmosphere,  clouds,  fogs  floating  in  the  atmosphere  ; 
and  rain,  snow,  hail,  dew,  and  frost  as  it  leaves  the  atmos- 
phere again.  The  weather  is  almost  constantly  changing. 
We  say  "  It  is  cold  to-day  "  or  "It  is  sultry  to-day  " 
according  as  the  conditions  of  the  atmosphere  are  such  as 
to  produce  the  one  effect  or  the  other.  The  average  of 
the  weather  conditions  for  a  given  place  is  the  climate  of 
the  place. 

Functions  of  the  Air.  —  The  atmosphere  is  of  vital 
importance  and  serves  us  in  a  number  of  important  func- 
tions :  (1)  It  supports  life  in  various  ways ;  (2)  it  conducts 
sound ;  (3)  it  transfers  and  distributes  heat,  and  also 
acts  as  a  non-conductor  of  heat  under  certain  conditions ; 
(4)  it  diffuses  light ;  (5)  it  supports  combustion ;  (6)  it 
drives  wind-power  machines ;  (7)  it  exerts  a  buoyant 
force  on  all  objects  immersed  in  it,  thus  enabling  some 

162 


WEATHER  153 

animals  to  fly  and  balloons  to  rise  from  the  surface  of  the 
earth ;  (8)  it  distributes  moisture ;  (9)  it  produces 
waves  and  ocean  currents ;  (10)  it  is  an  important  factor 
in  weathering  and  has  many  other  functions. 

The  atmosphere  as  we  consider  it  in  studying  weather 
includes  much  more  than  simply  the  mixture  of  the  gases, 
nitrogen  and  oxygen.  It  includes  all  the  various  sub- 
stances floating  in  it,  such  as  dust  particles  and  minute 
organisms  in  the  form  of  bacteria,  microbes,  and  decayed 
plant  and  animal  tissue.  The  dust  of  the  air  is  thought 
to  be  important  in  the  precipitation  of  moisture.  The 
minute  dust  particle,  by  virtue  of  the  law  of  gravitation, 
becomes  the  nucleus  of  condensation.  This  little  particle 
of  moisture  increases  in  size  until  it  forms  a  raindrop  or 
snowflake  and  then  falls  to  the  ground. 

Colors  of  the  Atmosphere.  —  On  clear  days  the  sky 
has  a  beautiful  blue  color.  This  color  is  due  to  the  break- 
ing up  of  the  sunlight  by  the  countless  number  of  small 
particles  floating  in  the  air.  If  the  particles  are  quite 
large,  other  colors  are  produced.  The  smoke  from  the 
lighted  end  of  a  cigar  is  blue  because  the  particles  in  the 
smoke  are  very  minute.  The  smoke  particles  from  the 
other  end  of  the  cigar,  however,  are  increased  in  size  by 
the  moisture  from  the  smoker's  mouth,  and  a  dull  grayish 
color  is  the  result.  Red  and  yellow  colors  predominate 
in  the  sky  near  sunrise  and  sunset,  because  the  sunlight 
passes  obliquely  through  a  great  thickness  of  atmosphere 
near  the  earth's  surface  and  the  other  colors  are  sifted  out 
by  the  large  particles  of  dust  which  float  near  the  ground. 

The  twilight  arch,  a  rosy  arch  of  lighted  air,  may  be 
seen  in  the  east  after  a  clear  sunset  as  the  sun  sinks  below 
the  horizon.  As  the  sun  sinks  lower  and  lower  this  arch 
rises  until  it  vanishes  in  the  darkening  shadow  of  night. 


154  GENERAL  SCIENCE 

Air  Density.  —  If  the  earth's  surface  had  the  same 
temperature  at  every  point,  the  air  near  this  surface 
would  have  the  same  density.  With  the  varying  degrees 
of  temperature  of  the  surface,  the  air  becomes  heated  in 
certain  places  and  then  being  less  dense  is  forced  up  by 
the  heavier  cold  air  around  it,  just  as  a  cork  released  at 
the  bottom  of  a  basin  of  water  is  forced  up  by  the  heavier 
substance  surrounding  it.  Air  also  becomes  lighter  as  it 
absorbs  moisture  or  water  vapor,  since  steam  has  a  lower 
density  than  air. 

For  measuring  the  pressure  of  the  atmosphere,  the 
barometer  is  used.  This  instrument  has  been  described 
in  Chapter  V.  It  should  be  observed  that  the  barom- 
eter does  nothing  more  than  indicate  the  air  pressure, 
and  this  with  other  facts  enables  the  forecaster  to  predict 
changes  in  the  weather. 

Isobars.  —  In  order  to  forecast  weather  conditions,  it 
is  necessary  to  compare  barometric  readings  from  many 
different  parts  of  the  country.  Since  barometric  readings 
vary  with  the  elevation  and  the  temperature,  in  order 
to  make  intelligent  comparisons  it  is  necessary  to  make 
corrections  for  these  differences  in  elevation  and  tempera- 
ture. By  the  aid  of  prepared  tables  this  is  readily  done, 
all  readings  being  reduced  to  the  corresponding  reading  at 
the  elevation  of  sea  level  and  the  temperature  of  the 
freezing  point  of  water.  After  the  corrections  are  made 
lines  are  drawn  connecting  points  having  equal  atmos- 
pheric pressure.  These  lines  are  called  isobars.  A  map 
showing  lines  of  equal  pressure  is  called  an  isobaric  map. 
On  the  daily  weather  map  isobars  (continuous  black  lines) 
are  drawn  representing  variations  in  pressure  of  one  tenth 
of  an  inch.  See  Figure  132. 

An  examination  of  several  daily  weather  maps  will 


WEATHER 


155 


156  GENERAL  SCIENCE 

show  that*  the  isobars  usually  run  in  concentric  lines 
around  areas  marked  in  some  cases  high  pressure,  and 
in  other  cases  low  pressure.  The  atmosphere  tends  to 
move  from  high  to  low  pressure,  and  the  greater  the 
difference  between  the  high  and  the  low  pressure  the  faster 
will  be  the  movement  of  the  air  or  the  higher  will  be  the 
wind  velocity.  This  may  be  tested  by  comparing  the 
weather  maps  on  a  windy  day  with  the  weather  maps  on 
a  calm  day. 

Atmospheric  Temperature.  —  A  very  small  amount  of 
heat  comes  from  the  stars,  but  the  sun  is  the  real  source 
of  nearly  all  the  heat  of  the  earth's  surface.  The  atmos- 
phere absorbs  a  small  part  of  the  heat  of  the  sun's  rays 
as  they  first  pass  through  it,  while  the  remainder  is  inter- 
cepted by  the  earth.  Here  it  is  partly  absorbed  and 
partly  reflected  back  into  the  atmosphere.  The  propor- 
tion of  the  rays  absorbed  to  those  reflected  varies  with 
different  parts  of  the  earth's  surface.  Much  more  heat  is 
reflected  from  water  than  from  soil,  and  an  increasing 
proportion  is  reflected  as  the  angle  of  incidence  of  the 
rays  increases.  When  the  rays  are  vertical,  the  greatest 
percentage  of  the  incident  radiant  heat  is  absorbed ;  this 
gradually  decreases  until  at  sunset  nearly  all  the  heat  is 
reflected.  The  reflected  radiant  heat  aids  in  warming 
the  air,  but  most  of  the  heat  of  the  atmosphere  is  received 
by  conduction  from  the  earth.  The  lower  portions  of  the 
atmosphere  absorb  heat  much  better  than  the  higher 
portions  for  the  reasons  that  the  air  near  the  earth  is 
more  dense  and  is  also  filled  with  impurities,  such  as  dust, 
heavy  gases,  and  water  vapor,  which  absorb  heat  readily. 
Each  little  particle  of  dust  in  the  atmosphere  becomes  a 
secondary  source  of  heat  and  heats  the  air  around  it. 
As  the  lower  layer  of  the  atmosphere  becomes  heated, 


WEATHER 


157 


convection  currents  are  produced  which  distribute  the 
heated  portions  throughout  the  whole  atmosphere. 

The  air  is  also  heated  by  compression  and  by  precipi- 
tation. We  have  learned  that  air  becomes  heated  when 
compressed,  as  in  the  chamber  of  a  bicycle  pump.  As  air 
descends  from  the  higher  altitudes,  as  from  the  mountain 
sides  to  the  valleys  below,  it  is  compressed  and  warmed. 
As  it  ascends  it  expands  and  becomes  colder,  about  1°  C. 
for  every  550  feet  of  ascent.  This  heating  of  the  air  by 


/u 
6O° 
50° 
40° 
30° 
20° 
10 
n° 

f 

""*"' 

X 

/ 

J 

•-~^- 

\ 

—          w 

~12      2      4       6       8      10     IZ     Z      4      6       8       1O     12 

O'CLOCK  NOON  MIDNIGHT 

MIDNIGHT 

FIG.  133.  —  Temperature  Curve  Showing  Variation  in  Temperature. 

compression  and  cooling  by  expansion  is  known  as  adia- 
batic  heating  and  cooling. 

Air  is  being  warmed  in  areas  of  high  pressure  and  cooled 
in  areas  of  low  pressure,  and  it  may  seem  at  first  as  though 
the  air  should  be  warmer  in  areas  of  high  pressure  than  in 
areas  of  low  pressure.  This  is  not  the  case.  The  reason 
for  the  low  pressure  is  that  the  area  is  warmer ;  hence  the 
air  is  lighter.  Although  the  expansion  of  air  is  a  cooling 
process,  the  effect  is  more  than  counteracted  by  the  heat 


158 


GENERAL  SCIENCE 


it  receives  by  conduction  from  the  earth.  The  energy 
required  to  change  water  to  vapor  appears  again  in  the 
form  of  heat  when  the  vapor  changes  back  to  water  and 
falls  as  rain.  This  heat  is  considerable,  536  calories  for 
each  gram  of  water.  With  snow  the  effect  is  still  more 
noticeable.  Why? 

Not  all  the  heat  which  reaches  the  earth  is  retained. 
A  large  part  of  that  which  is  reflected  and  radiated  by  the 
earth  passes  back  through  the  atmosphere  into  the  endless 
space  beyond. 

Thermograph.  —  Figure  133  shows  a  temperature  curve 
or  a  record  of  the  variation  in  temperature  of  a  given 


Flat  bulb  filled 
with  alcohol 

FIG.  134.  — Thermograph. 

This  instrument  is  so  constructed  that  the  temperature  is  recorded 
automatically. 

place  for  a  given  length  of  time.  Such  a  curve  may  be 
produced  automatically  with  great  accuracy  by  a  thermo- 
graph (Figure  134). 

Experiment  47.  —  Take  four  or  more  thermometer  readings  at 
the  same  time  each  day  for  one  week  and  plot  the  temperature 
curve. 

Isotherms.  —  Lines  which  are  drawn  on  the  weather 
maps  connecting  points  having  the  same  temperature 
are  called  isotherms.  There  is  considerable  variation  in 


WEATHER  159 

the  position  of  isotherms  from  day  to  day,  as  will  be  seen 
by  consulting  the  daily  weather  maps.  If  these  lines  are 
averaged  for  a  certain  number  of  days,  the  result  will  be 
the  mean  temperature  for  that  period  of  time.  Figure 
135  shows  an  isothermal  map  for  July,  Figure  136  one  for 
January,  and  Figure  137  shows  a  chart  of  the  mean  annual 
temperatures  for  the  year.  On  consulting  these  charts 
it  will  be  noticed  that  the  isotherms  of  70  degrees  lie  at 
some  distance  on  either  side  of  the  equator,  but  that  the 
distances  for  July  and  January  are  not  the  same.  These 
isotherms  form  the  boundaries  of  the  hot  zone  through 
which  runs  the  heat  equator  or  the  line  of  highest  tempera- 
ture. It  lies  north  of  the  true  equator  in  July  and  south 
of  it  in  January.  The  temperate  zone  is  the  belt  inclosed 
between  the  isotherms  of  70  degrees  and  30  degrees. 
Beyond  30  degrees  lie  the  frigid  zones.  These  zones 
follow  the  movements  of  the  heat  equator  and  are  not 
fixed  belts. 

Change  of  Temperature  with  the  Seasons.  —  As  the 
earth  moves  in  its  orbit  around  the  sun,  there  are  six 
months  in  each  year  in  which  the  northern  hemisphere  is 
inclined  toward  the  sun  and  six  months  in  which  it  is 
inclined  away  from  the  sun.  In  the  months  in  which 
it  is  inclined  toward  the  sun  it  gains  more  heat  by  absorp- 
tion during  the  long  days  than  it  loses  by  radiation  during 
the  short  nights,  and  the  temperature  rises  above  the 
average  temperature  for  the  year.  The  opposite  is  true 
of  the  southern  hemisphere  during  this  period.  During  the 
other  six  months  of  the  year  the  northern  hemisphere 
is  inclined  away  from  the  sun  and  the  southern  hemisphere 
toward  the  sun,  with  the  result  that  the  southern  hemi- 
sphere is  then  the  summer  hemisphere  and  the  northern 
the  winter  hemisphere. 


160 


GENERAL  SCIENCE 


WEATHER 


161 


162 


GENERAL  SCIENCE 


WEATHER 


163 


Movements  of  the  Atmosphere.  —  Movements  of  the 
air  are  caused  by  the  force  of  gravity  wherever  differences 
in  atmospheric  pressure  exist.  These  j 

differences  are  due  to  the  differences  in 
the  temperature  of  the  air,  at  any  area 
of  low  pressure  the  heavier  air  from  all 
sides  forcing  up  the  lighter  air.  A  simple 
experiment  may  be  performed  to  show 
the  origin  of  the  winds. 

Experiment  48.  —  Cut  a  piece  of  paper  in 
the  form  of  a  spiral  (Figure  138)  and  hold  it 
over  a  lighted  Bunsen  burner.  The  rapid  up- 
ward current  of  the  air  will  cause  the  spiral  to 
turn,  while  colder  air  will  be  moving  toward  the 
flame,  as  shown  in  the  diagram.  ;  FIG.  138. 

The  horizontal  movements  of  the  air  are  called  winds, 
when  the  movements  are  strong  enough  to  be  perceptible. 
The  vertical  movements  are  called  calms.  To  summarize : 

1 .   Winds  are  caused  by  the  force  of  gravity ; 

2.  Winds  blow  from  re- 
gions of  high  barometric 
pressure  to  regions  of  low 
pressure. 

3.  The  velocity  of  the 
wind   depends  upon  the 
barometric  gradient.   The 
steeper  the  grade,  or  the 
greater  the  difference  in 
pressure    between    two 
areas  the  greater  will  be 
the  velocity  of  the  wind. 

FIG.    139. -The   Anemometer    an   In-         Figure      139     shoWS     an 

strument  for  Determining  the  Velocity  of 

the  Wind.  instrument  which  is  used 


164  GENERAL  SCIENCE 

to  measure  the  velocity  of  the  wind,  the  anemometer. 
The  speed  with  which  it  revolves  is  registered  as  a  certain 
number  of  miles  per  hour. 

For  purposes  of  classification  winds  may  be  grouped 
into  terrestrial,  cyclonic,  and  continental  winds. 

Terrestrial  or  Planetary  Winds.  —  On  all  the  planets 
which  have  an  atmosphere,  there  are  winds  which  are  due 
to  the  fact  that  the  planet  rotates  and  that  it  is  heated 
from  some  external  source.  On  the  earth  the  strength 
of  these  winds  and  the  boundaries  of  the  wind  belts  vary 
with  the  seasons.  The  air  is  heated  in  the  region  of  the  heat 
equator  and  moves  up,  thus  producing  a  low  pressure  belt 
at  the  equator  and  a  high  pressure  belt  near  the  tropics 
(Figure  140). 

The  low  pressure  belt  caused  by  the  ascending  air  is 
known  as  the  equatorial  calms  or  the  doldrums,  and  the 
high  pressure  belts  caused  by  the  descending  air  are  known 
as  horse  latitudes. 

The  winds  which  blow  from  the  regions  of  the  horse 
latitudes  or  tropical  calms  toward  the  equator  are  called 
trade  winds,  so  named  because  of  the  regularity  with 
which  they  blow.  In  the  days  of  sailing  vessels  they 
were  important  factors  in  navigation.  The  trade  winds 
do  not  blow  directly  north  and  south  but  are  deflected 
toward  the  west  by  the  rotation  of  the  earth. 

The  anti-trade  winds  are  those  currents  of  air  which  are 
high  above  the  trade  winds  and  blow  in  the  opposite 
direction.  -It  is  the  descent  of  these  winds  which  pro- 
duces the  tropical  winds  or  horse  latitudes. 

The  prevailing  westerlies  are  the  winds  which  blow 
from  the  horse  latitudes  toward  the  poles.  Like  the 
trade  winds  their  course  is  affected  by  the  shape  and 
rotation  of  the  earth ;  they  move  northeast  in  the  north- 


WEATHER 


165 


Winds  and  Kains  of  July  —  Northern  S 


FIG.  140.  —  Terrestrial  Wind  Belts  in  Summer  and  Winter.     The  Heat 
Equator  Lies  in  the  Midst  of  the  Equatorial  Rain  Belt. 

ern  hemisphere  and  southeast  in  the  southern  hemi- 
sphere. These  winds  are  usually  a  part  of  the  great  whirls 
known  as  cyclones  and  anti-cyclones  and  are  subject  to 
frequent  changes  in  direction. 

Cyclonic  Winds.  —  Because  of  the  rotation  and  shape 
of  the  earth,  air  flows  toward  a  low  pressure  area  by  a 


166  GENERAL  SCIENCE 

curved  route.  The  winds  coming  from  all  sides  from 
similarly  curved  routes  set  the  air  at  the  center  in  a  whirl. 
These  cyclonic  whirls  cover  large  areas,  being  frequently 
1000  miles  or  more  in  diameter.  They  should  not 
be  confused  with  the  violent  whirling  storms  which 
are  so  commonly  called  cyclones.  Such  storms  are 
properly  called  tornadoes  (see  United  States  weather  map 
showing  cyclonic  (low)  and  anti-cyclonic  (high)  areas) 
(Figure  141). 

In  the  northern  hemisphere  the  direction  of  the  rotation 
of  the  air  in  a  cyclonic  whirl  is  opposite  to  that  of  the  hands 
of  a  clock.  In  the  southern  hemisphere  the  direction  is 
the  same  as  that  of  the  hands  of  a  clock. 

The  general  direction  in  which  the  whole  cyclonic  area 
moves  is  from  west  toward  the  east  in  the1  United  States. 
Sometimes  cyclones  enter  the  United  States  from  south- 
western Canada  and  travel  southeast  to  the  Mississippi 
valley  and  then  northeast  to  the  Atlantic  Ocean.  Some- 
times they  njove  almost  due  east  across  the  continent  and 
at  other  times  they  develop  in  the  southwest  and  move  in  a 
northeasterly  direction.  They  travel  at  varying  rates  of 
speed,  averaging  600  to  700  miles  a  day. 

An  anti-cyclone  is  an  area  of  high  pressure.  It  is  the 
opposite  of  a  cyclone,  the  winds  blowing  away  from  the 
center  instead  of  toward  the  center. 

Hurricanes.  —  Very  violent  storms,  known  as  hurricanes 
in  the  Atlantic  Ocean  and  typhoons  in  the  Pacific  Ocean, 
occasionally  develop  in  the  doldrums.  They  grow  to  be 
several  hundred  miles  in  diameter  and  are  accompanied 
by  violent  winds,  which  whirl  in  great  spirals  around 
an  area  of  low  pressure  and  an  enormous  fall  of  rain. 
They  usually  come  when  the  heat  equator  is  farthest  from 
the  geographical  equator.  They  occur  in  the  Atlantic 


WEATHER 


167 


168 


GENERAL  SCIENCE 


Ocean  in  the  region  of  the  West  Indies ;  in  the  Pacific 
Ocean  near  the  Philippines  and  Japan  ;  and  in  the  Indian 
Ocean  near  India  and  also  the  Island  of  Madagascar.  It 
will  be  observed  that  they  occur  in  relatively  the  same 
positions  in  the  two  oceans.  They  travel  in  a  curve  first 
toward  the  northwest,  gradually  turning  until,  as  they 
enter  the  temperate  zone,  the  direction  is  northeast. 


FIG.  142.  —  The  Path  of  the  Galveston  Hurricane. 

The.  sea  floods  which  devastated  Galveston,  Texas,  in 
September,  1900,  were  caused  by  a  hurricane  (Figure  142). 
The  wind  was  so  violent  that  the  waters  from  the  Gulf  of 
Mexico  were  forced  into  the  streets  of  the  city,  doing 
great  damage.  In  the  lowlands  at  the  head  of  the  Bay 
of  Bengal  thousands  of  people  have  lost  their  lives  in  the 
sea  floods  caused  by  the  oft-recurring  typhoons  of  the 
Indian  Ocean.  The  damage  done  by  the  wind  and  rain 
to  shipping  and  plantations  is  also  very  great,  frequently 


WEATHER  169 

driving  vessels  ashore  and  stripping  plantations  of  every 
vestige  of  usable  plant  growth. 

Tornadoes  differ  from  hurricanes  and  typhoons  in 
duration  and  area  affected.  They  originate  in  the  region 
of  the  prevailing  westerlies  and  are  quite  common  in  the 
plains  in  the  western  Mississippi  valley.  Their  diameter 
varies  from  a  few  feet  to  a  mile  or  even  more,  but  the 
violent,  destructive  effects  are  usually  confined  to  a  path 


U.  S.  Weather  Bureau. 
FIG.  143.  — A  Tornado  Cloud  as  Seen  from  Pierre,  South  Dakota,  in  July,  1910. 

a  few  rods  wide.  In  the  summer  season  they  are  often 
associated  with  thunderstorms.  As  they  approach  they 
have  the  appearance  of  a  funnel-shaped  cloud  hanging  from 
the  black  mass  of  thunder  cloud  above  (Figure  143) .  They 
are  the  most  violent  storms  which  occur  in  the  United 
States.  As  a  tornado  approaches,  a  low  roar  which  in- 
creases momentarily  in  intensity  is  heard.  Thunder,  light- 
ning, rain,  and  hail  blend  to  make  the  effect  more  terrible. 
Buildings  that  lie  in  the  path  of  such  a  storm  are  scattered 


170 


GENERAL  SCIENCE 


in  all  directions  (Figure  144).  Trees  are  uprooted  and 
whirled  about  like  feathers.  Some  of  the  effects,  such  as 
driving  straws  through  pine  boards  and  removing  the 
feathers  from  chickens,  are  almost  incredible.  Such  storms 
move  forward  at  the  average  rate  of  about  thirty  miles 


U.  S.  Weather  Bureau. 
FIG.  144.  —  A  House  Wrecked  by  a  Tornado  at   Binghamton,  N.  Y. 

an  hour,  but  the  rotary  speed  of  the  air  in  the  whirls  may 
reach  a  velocity  of  500  miles  an  hour. 

The  centrifugal  force  of  the  rapidly  whirling  mass  is 
sufficient  to  produce  an  area  of  very  low  pressure.  As  a 
tornado  passes  over  a  lake  or  the  ocean,  a  column  known 
as  a  water  spout  sometimes  forms  in  the  vortex  (Figure 
145) .  Some  scientists  hold  the  opinion  that  the  water  spout 
is  formed  by  water  which  is  drawn  up  from  the  ocean  into 
the  vortex  of  the  whirl,  while  others  think  that  the  water 
comes  from  the  clouds. 


WEATHER 


171 


Winds  with  Special  Names.  —  The  inflowing  winds  of 
cyclonic  storms  are  sometimes  given  special  names  in 
different  parts  of  the  world.  The  hot,  scorching  winds 
which  blow  from  the  African  desert  across  Italy  are  called 
siroccos,  and  the  name  is  now  often  applied  to  any  south 
winds  which  are  very  hot  and  dry.  In  southern  Australia 
such  winds  are  called  brickfielders  because  they  bake  the 


V.  S.  Weather  Bureau. 


FIG.  145.  —  Waterspout  at  Vineyard  Sound,  August  19,  1896. 

fields  until  they  are  like  bricks.  The  chinook  is  the  wind 
that  blows  from  the  Rocky  Mountains  toward  the  Missis- 
sippi valle}^.  It  has  lost  its  moisture  on  the  western  slope 
of  the  Rocky  Mountains,  and  as  it  descends  and  is  warmed 
its  capacity  for  holding  moisture  is  greatly  increased, 
with  the  result  that  it  takes  up  the  moisture  from  the 
fields  instead  of  bringing  moisture  to  them.  The  blizzard 
of  the  western  plains  is  an  especially  cold  wind  accom- 


172 


GENERAL  SCIENCE 


panied  by  snow.     The  norther  of  Texas  and  the  buran  of 
Siberia  are  simply  local  names  for  cold  winds. 

Monsoons.  —  If  land  is  located  with  reference  to  the 
belt  over  which  the  equatorial  calms  move  so  that  the 
heat  equator  is  over  the  land  for  a  part  of  the  year  and 
over  the  adjacent  water  the  remainder  of  the  year,  mon- 
soons are  developed.  That  is,  the  trade  winds  will 
blow  from  the  sea  toward  the  land  for  a  part  of  the  year 


FIG.  146.  —  Southern  Asia,  Showing  the  Monsoon  Region  and  the  Region 
of  Heavy  Rainfall. 

The  arrows  indicata  the  direction  of  the  wind  during  July  and  August  (the  left- 
hand  illustration)  and  January  and  February  (the  right-hand  illustration) . 

and  from  the  land  toward  the  sea  the  remainder  of  the  year. 
The  best-known  monsoon  winds  are  in  the  region  of  India, 
where  the  sea  breeze  in  summer  is  so  strong  that  it  reaches 
the  southern  slopes  of  the  Himalayas  (Figure  146).  As  the 
wind  passes  over  the  warm  seas  it  becomes  laden  with  mois- 
ture, which  is  precipitated  as  the  air  is  cooled  on  the  moun- 
tain sides.  The  rainfall  here  is  enormous,  in  some  places 
amounting  to  as  much  as  500  inches  a  year.  As  the  heat 
equator  moves  south,  the  direction  of  these  winds  is 
reversed.  Since  they  are  warmed  as  they  descend  they 


WEATHER  173 

take  up  moisture  instead  of  precipitating  it,  thus  pro- 
ducing a  period  of  drouth  in  the  land.  Thousands  of 
lives  have  been  lost  in  the  famines  following  the  winds. 

Land  and  sea  breezes  occur  along  the  coast  of  large 
bodies  of  water.  During  the  daytime  the  land  is  heated 
more  rapidly  than  the  water,  the  specific  heat  of  water 
being  much  greater  than  that  of  the  earth.  The  Hot  air 
over  the  land  expands  and  becomes  lighter,  and  the  heavier 
air  from  the  ocean  forces  it  up  and  takes  its  place.  This 
is  the  sea  breeze  which  blows  during  the  daytime  and 
reaches  its  maximum  strength  usually  late  in  the  after- 
noon. At  night  the  earth  cools  more  rapidly  than  the  sea, 
and  in  a  short  time  the  sea  is  warmer  than  the  land  and  the 
current  of  air  is  reversed.  This  is  the  land  breeze  which 
blows  during  the  night  and  reaches  its  maximum  toward 
morning.  These  winds  are  more  noticeable  in  the  tropics, 
since  the  change  in  temperature  is  greatest  there. 

Humidity  and  Precipitation.  —  Water  vapor  is  always 
present  in  the  atmosphere ;  the  amount,  however,  varies 
greatly.  The  relative  humidity,  or  degree  of  saturation, 
of  the  atmosphere  is  defined  as  the  ratio  between  the 
amount  of  moisture  actually  present  in  a  given  volume  of 
air  and  the  amount  which  would  be  present  if  the  air  were 
saturated.  When  air  contains  all  the  moisture  that  it  can 
hold  at  a  given  temperature,  it  is  said  to  be  saturated. 
Air  over  the  ocean  is  usually  quite  near  a  state  of  satura- 
tion. As  a  usual  thing  we  can  tell  something  of  the 
humidity  of  the  atmosphere  without  the  aid  of  scientific 
instruments.  When  the  air  contains  a  large  amount  of 
water  vapor  and  feels  damp,  we  say  the  humidity  is  high. 
When  it  contains  little  vapor  and  feels  dry,  the  humidity 
is  low.  Dry  air  is  more  invigorating  than  damp  air,  since 
it  produces  active  evaporation  of  the  perspiration  of  the 


174  GENERAL  SCIENCE 

body.  If  the  air  is  warm  and  damp  we  say  it  is  "  close  " 
or  sultry.  Cold,  damp  air  is  penetrating  and  "  raw." 

As  air  is  warmed,  its  capacity  for  retaining  moisture  is 
increased  ;  and  the  reverse  is  true  if  it  be  cooled.  If  we 
cool  air  having  a  relative  humidity  of  80,  it  will  soon 
reach  a  temperature  at  which  it  is  saturated  or  has  a 
relative  humidity  of  100  per  cent.  If  it  be  cooled  further, 
some  of  its  moisture  will  be  precipitated  as  dew,  rain,  or 
some  other  form  of  precipitation.  If  we  heat  air,  the 
relative  humidity  will  be  reduced.  If  we  cool  it,  the 
relative  humidity  will  be  increased. 

Dew  Point.  -  -  The  temperature  of  air  at  its  point  of 
saturation  is  the  dew  point. 

Experiment  49.  —  Fill  a  polished  metal  cup  with  water  and 
stir  it  with  a  thermometer  as  ice  is  added  slowly.  The  temperature 
at  which  a  film  of  moisture  forms  on  the  outside  of  the  cup  is  the 
dew  point  of  the  air  surrounding  the  cup. 

We  have  often  noticed  the  "  sweating  "  of  pitchers  con- 
taining ice  water.  This  simply  means  that  the  air  sur- 
rounding the  pitcher  has  been  cooled  below  its  dew  point, 
and  some  of  its  moisture  must  be  deposited. 

The  dew  point  apparatus  may  be  used  to  determine  the 
relative  humidity  of  the  atmosphere,  since  the  ratio  be- 
tween the  amount  of  moisture  present  in  the  air  and  the 
amount  which  would  be  present  if  the  air  were  saturated 
is  the  same  as  the  ratio  between  the  pressure  which  the 
water  vapor  in  the  air  exerts  and  the  pressure  which  it 
would  exert  if  the  air  were  in  a  saturated  condition.  For 
example,  let  us  suppose  that  the  dew  point  of  the  air  in  a 
room  be  12°  and  the  temperature  of  the  air  in  the  room  be 
25°.  The  amount  of  moisture  in  the  air  is  enough  to 
saturate  it  at  the  temperature  of  12°.  By  referring  to  the 
Appendix,  Table  I,  we  find  that  the  pressure  of  water 


WEATHER  175 

vapor  at  12°  C.  is  10.5  millimeters.  Hence  the  air  con- 
tains 10.5/23.5  or  .447  as  much  water  vapor  as  it  is  capable 
of  holding.  The  relative  humidity  is  44.7  per  cent. 

Humidity  determinations  have  a  practical  value  in  that 
they  enable  us  better  to  predict  weather  conditions  and  to 
have  proper  conditions  in  public  buildings,  schools,  and 
homes.  For  the  most  healthful  conditions  the  relative 
humidity  should  be  from  50  per  cent  to  60  per  cent. 

Dew  and  Frost.  —  Dew  is  a  deposit  of  moisture  from 
the  air  upon  the  ground,  grass,  stones,  and  other  objects 
near  the  ground.  After  sunset  these  objects  radiate  their 
heat  very  rapidly  and  soon  become  quite  cold.  The  air 
which  comes  in  contact  with  them  is  cooled  below  the  dew 
point  and  some  of  its  moisture  is  deposited.  If  their 
temperature  is  below  the  freezing  point  of  water,  frost  is 
formed  instead  of  dew.  Dew  and  frost  are  formed  most 
rapidly  on  the  surfaces  of  substances  which  are  the  best 
radiators  of  heat. 

Clouds  are  not  favorable  to  the  formation  of  dew,  since 
they  act  as  a  blanket  over  the  earth  and  prevent  the 
radiation  of  its  heat.  Some  of  the  rural  weather  prophets 
consider,  the  absence  of  dew  as  a  "  sign  "  of  rain.  It  is  an 
indication  that  there  were  clouds  during  the  night  or  a 
relatively  high  humidity  of  the  atmosphere.  Strong 
winds  also  are  unfavorable  to  the  formation  of  dew,  since 
the  air  does  not  remain  long  enough  in  contact  with  the  cool 
objects  to  be  cooled  to  its  dew  point  and  deposit  moisture. 

Clouds.  —  Clouds  are  formed  by  the  condensation  of 
the  moisture  in  the  air.  If  a  cloud  meets  the  surface  of 
the  earth,  it  is  called  a  fog,  and  other  names  are  applied 
to  it  according  to  the  manner  of  its  formation,  its  shape, 
its  color  and  appearance,  and  its  elevation.  The  more 
common  forms  are  the  cumulus,  the  cirrus,  the  stratus, 


176  GENERAL  SCIENCE 

and  the  nimbus.  In  the  daytime  of  fair  summer  weather 
ascending  convection  currents  are  produced  in  the  atmos- 
phere. The  air  expands  and  cools  as  it  rises.  If  the  cool- 
ing continues  until -the  dew  point  is  reached,  some  of  the 
vapor  is  condensed,  forming  great  masses  of  fleecy  clouds 
which  appear  like  the  lightest  wool  in  the  sunshine. 
These  clouds  are  very  irregular  in  shape,  and  their  tops 
are  constantly  changing.  Their  bases  are  more  regular 


FIG.  147.  —  Cumulus  Clouds. 

and  float  in  the  air  at  the  height  of  1000  feet  to  2500 
feet.  These  clouds  are  called  cumulus  clouds  (Figure 
147).  They  are  usually  seen  from  the  middle  of  the  fore- 
noon to  the  middle  of  the  afternoon,  when  they  dissolve 
and  disappear. 

Cirrus  Clouds.  —  Quite  commonly  an  advancing  cyclone 
is  preceded  by  plumelike  strips  of  pale,  whitish  cloud  (Fig- 
ure 148),  often  five  or  ten  miles  high.  These  clouds  are 
formed  in  the  currents  of  air  that  flow  out  and  forward 
from  the  upper  part  of  the  storm  and  they  move  quite 


WEATHER  177 

steadily  forward  with  the  area  of  low  pressure.  On 
account  of  their  great  height  they  consist  of  minute  ice 
crystals.  If  the  cloud  spreads  out  in  a  thin  sheet,  it 
is  called  a  cirrostratus.  When  we  look  at  the  sun  or 
moon  through  such  a  cloud,  we  have  the  familiar  "  ring 
around  the  moon  "  or  "  ring  around  the  sun  "  phenom- 
enon. Such  a  ring  is  called  a  halo  and  is  formed  by  the 
refraction  of  the  light  in  passing  through  the  ice  crystals. 


FIG.  148.  —  Cirrus  Clouds. 

Stratus  clouds  are  frequently  seen  near  the  horizon  in 
the  late  afternoon  or  early  morning.  They  occur  in  long 
narrow  bands  (Figure  149)  or  strata.  Nimbus  is  the  name 
applied  to  the  dark  gray  rain  cloud.  These  clouds  usually 
occupy  the  whole  central  portion  of  a  cyclonic  storm  and 
often  have  an  area  of  many  thousand  square  miles.  Their 
height  above  the  surface  of  the  earth  varies  with  condi- 
tions, but  they  are  often  but  a  few  hundred  feet  above 
our  heads.  In  winter  they  are  especially  large  and  dense 


178  GENERAL  SCIENCE 

and  sometimes  remain  over  a  certain  area  for  several 
days.  Nimbus  clouds  have  no  especial  form,  and  the 
term  is  sometimes  applied  to  any  storm  cloud. 

Rainfall.  —  The  term  "rainfall"  includes  all  forms  of 
precipitation  —  rain,  snow,  hail,  and  sleet.  Rain  occurs 
when  the  moisture  condenses  in  drops  large  enough  to 
fall  to  the  earth.  Snow  is  formed  when  the  moisture  of 
the  air  is  condensed  at  temperatures  below  the  freezing 


FIG.  149.  —  Stratus  Clouds. 

point,  0°  C.  Sometimes  moisture  condenses  as  snow  in 
the  higher  atmosphere  and  then  melts  as  it  falls  through 
the  warmer,  lower  atmosphere,  reaching  the  earth  as 
rain.  Hail  occurs  chiefly  during  thunderstorms  in 
summer,  when  the  raindrops  are  frozen  on  their  way  to 
the  earth.  There  are  several  theories  to  account  for  the 
formation  of  hailstones  in  concentric  layers,  but  it  is  quite 
probable  that  the  ascending  air  currents  of  high  thunder- 
storm clouds  carry  the  raindrops  up  into  a  region  of  quite 
low  temperature  and  that  as  they  fall  they  pass  through 


WEATHER 


179 


180 


GENERAL  SCIENCE 


several  air  currents  alternately  above  and  below  the  freez- 
ing point  of  water. 

The  distribution  of  rainfall  over  the  surface  of  the  earth 
(Figure  150)  shows  that  there  is  more  rainfall  in  the  tropical 
belts  and  in  regions  where  the  trade  winds  and  prevailing 
westerlies  ascend  the  mountain  slopes.  The  desert  regions 
are  the  lowlands  which  are  crossed  by  the  trade  winds,  or 
interior  regions  which  are  crossed  only  by  winds  that  have 
previously  lost  most  of  their  moisture.  Such  a  region  is 
found  just  east  of  the  Rocky  Mountains.  The  heaviest 
rainfall  in  the  world  occurs  on  the  land  bordering  the 
Bay  of  Bengal  and  the  southwest  coast  of  India,  where 
the  average  annual  rainfall  is  about  30  feet. 

Rainfall  is  measured   in   an   instrument  called  a  rain 

gauge.  Figure  151  shows  the 
rain  gauge  used  by  the  United 
States  Weather  Bureau.  An 
inch  of  rainfall  means  that  enough 
rain  has  fallen  to  cover  the  area 
considered  to  a  depth  of  one 
inch  of  water.  Snow  and  hail 
are  melted  before  the  measure- 
ments are  taken. 

Perform  the  experiment  to  de- 
termine how  many  inches  of  snow 
are  equivalent  to  one  inch  of 
rainfall. 

Thunderstorms  are  frequent 
in  the  United  States.  They 
commonly  occur  on  the  warmest  summer  days,  and  dur- 
ing the  warmest  parts  of  those  days.  The  first  indica- 
tion of  a  thunderstorm  is  usually  the  appearance  of  a 
heavy  cumulus  cloud  in  the  west.  The  original  cloud  is 


\ 


k  4 


FIG.  151 .  —  Rain  Gauge. 


Lightning. 


U.  S.  Weather  Bureau. 


181 


182  GENERAL  SCIENCE 

formed  in  the  ordinary  way ;  then  as  other  ascending 
currents  of  warm  air  strike  the  lower  part  of  the  cloud 
they  are  deflected  along  its  surface  and  cooled  so  that 
there  is  usually  a  heavy  downpour  of  rain.  The  duration 
of  the  storm  is  often  but  a  few  minutes,  though  sometimes 
it  continues  for  several  hours. 

When  water  is  condensed  rapidly  in  the  air,  electricity 

is  generated,  and  each 
particle  of  water  be- 
comes charged  with 
electricity.  Lightning 
is  due  to  the  passage 
of  a  large  electric 
spark  from  one  cloud 
to  another  or  from 
the  cloud  to  the 
ground  (Figure  152). 
Thunder  which  fol- 
lows the  flash  of  light- 
ning is  due  to  the  vibrations  in  the  air  along  the  path  of 
the  discharge.  It  is  possible  to  estimate  the  distance  of 
a  flash  of  lightning  by  observing  the  time  in  seconds 
that  elapses  between  a  flash  and  its  thunder  and  multiply- 
ing by  the  speed  of  sound  in  air.  The  velocity  of  light  is 
so  great  that  the  time  consumed  by  the  flash  in  travel- 
ing from  its  source  to  the  observer  may  be  neglected. 
Heat  lightning  is  lightning  at  such  a  great  distance  that 
the  thunder  accompanying  it  cannot  be  heard.  The 
flash  shows  merely  as  light  on  the  surrounding  clouds. 

At  the  heat  equator  heavy  rains  usually  accompanied 
by  thunder  and  lightning  occur  almost  daily.  These 
storms  give  the  name  "  rainy  season  "  to  the  time  of  year 
in  which  they  occur. 


WEATHER  183 

Weather  Changes.  —  We  have  learned  that  "  weather  " 
is  a  very  inclusive  term.  It  includes  all  the  atmospheric 
conditions  that  can  be  observed,  such  as  temperature, 
the  amount  and  kind  of  precipitation,  the  humidity  of  the 
air,  the  condition  of  the  sky  with  reference  to  the  clouds, 
and  the  direction  and  velocity  of  winds. 

In  the  torrid  zone  the  weather  is  quite  regular.  In  the 
temperate  zones  the  weather  changes  in  the  summer 
season  are  moderate,  but  in  winter  the  changes  occur  more 
often  and  cover  nearly  every  variety  of  "  weather,"  due 
to  the  occurrence  of  numerous  cyclonic  storms.  In  the 
frigid  latitudes  the  changes  are  not  quite  so  marked,  the 
temperature  being  very  cold  during  the  winter  season  and 
slightly  warmer  during  the  summer. 

Weather  Bureau. — A  large  number  of  observing  stations 
have  been  established  in  the  United  States  and  adjacent 
countries  for  the  purpose  of  making  systematic  observa- 
tions of  weather  conditions.  At  the  same  time  each  morn- 
ing and  evening  at  the  different  stations  a  record  is  made 
of  the  barometric  pressure,  temperature,  relative  hu- 
midity, the  direction  and  velocity  of  the  wind,-  the  appear- 
ance of  the  sky,  and  the  amount  of  rainfall.  This  informa- 
tion is  telegraphed  to  the  Weather  Bureau  at  Washington. 
From  these  reports,  weather  maps  showing  the  weather 
conditions  over  the  entire  United  States  are  printed. 
The  tabulated  information  is  sent  back  to  the  stations  in 
the  larger  cities,  and  a  smaller  map  is  printed  and  mailed 
throughout  the  section  in  which  the  substation  is  located. 
In  an  almost  incredibly  short  time  the  whole  country  has 
been  given  the  benefit  of  the  information  collected. 
From  the  map  it  is  quite  easy  for  the  novice  to  forecast 
the  weather  for  the  next  twenty-four  hours,  while  the 
trained  observer  will  be  able  to  forecast  the  weather  for  a 


184  GENERAL  SCIENCE 

week  or  even  more.  It  should  be  noted,  however,  that  the 
forecasts  are  made  for  large  areas  and  not  likely  to  prove 
correct  in  every  detail  for  every  locality.  The  movement 
of  areas  of  low  and  high  pressure  in  the  belt  of  prevailing 
westerlies  can  only  be  estimated.  Sometimes  they  in- 
crease in  speed  and  sometimes  decrease. 

The  information  given  out  by  the  Weather  Bureau  is 
of  great  value  to  farmers,  those  interested  in  shipping,  in 
fact  all  those  whose  business  or  pleasure  in  any  degree 
depends  upon  the  weather.  The  farmer  may  be  able  to 
save  his  grain  by  having  knowledge  of  an  approaching 
storm  or  his  crop  of  peaches  by  learning  of  a  coming  frost. 
Hurricanes  and  other  storms  often  do  much  damage  to 
shipping  and  would  do  much  more  if  it  were  not  for 
advance  information  which  enables  ships  to  move  out  of 
the  path  of  the  storm  to  seek  some  safe  harbor.  News  of 
a  cold  wave  enables  railroad  companies  and  commission 
merchants  to  save  their  patrons  a  great  deal,  since  many 
articles  of  food  such  as  fruit  and  vegetables  are  spoiled  by 
freezing  and  cannot  be  shipped  without  danger  of  loss  in 
cold  weather.  Flood  warnings  are  also  the  means  of 
saving  much  property  along  the  larger  rivers. 

It  can  usually  be  arranged  to  have  several  copies  of  the 
weather  maps  sent  to  the  school  by  applying  to  the  nearest 
Weather  Bureau  office  and  giving  assurance  that  the  maps 
will  be  properly  used. 

QUESTIONS 

1.  Why   does    low    barometer  usually  indicate  the  approach 
of  a  storm? 

2.  How  does  air  distribute  heat? 

3.  Why  do  balloons  float  lower  at  night  than  in  the  daytime? 

4.  Why  does  -a  rise  in  temperature  usually  follow  the  begin- 
ning of  a  snowstorm  ? 


WEATHER  185 

5.  Name  the  ways  in  which  the  air  serves  us. 

6.  What  becomes  of  the  fog  as  it  disappears  on  a  foggy  morn- 
ing? 

7.  Why  is   it   cold   on   the   mountain   tops   even   in  tropical 
countries? 

8.  Why  does  air  laden  with  dust  become  heated  more  rapidly 
than  clean  air? 

9.  Why  should  fruit  trees  be  planted  on  the  higher  ground 
rather  than  in  the  valleys  ? 

10.  How  is  air  heated? 

11.  How  does  the  shape  of  the  earth  affect  the  distribution  of 
temperature  ? 

12.  How  do  clouds  prevent  the  formation  of  dew  and  frost? 

13.  Why  does  covering  a  plant  with  paper  or  cloth  prevent  it 
from  being  frostbitten? 

14.  What  kind  of  soil  is  best  for  absorbing  heat? 

15.  What  is  the  effect  of  large  bodies  of  water  on  the  climate 
of  a  region? 

16.  What  is  the  relation  of  trade  winds  to  rainfall? 

17.  Will  the  pressure  in  an  ascending  column  of  air  be  low  or 
high? 

18.  Does  moisture  in  the  air  make  the  air  heavier?      Why? 

19.  What  is  relative  humidity?     How  may  it  be  determined ? 

20.  Is  it  correct  to  say  that  snow  is  frozen  rain? 

21.  What  is  the  difference  between  a  fog  and  a  cloud? 

22.  Define  meteorology. 

23.  How  does  humidity  vary  with  the  temperature? 

24.  Where  is  the  heaviest  rainfall  in  the  United  States? 


CHAPTER   XI 
MAGNETISM   AND   ELECTRICITY 

Magnets.  —  Many  years  ago  it  was  observed  that  an 
occasional  piece  of  ore  possessed  the  property  of  attract- 
ing small  bits  of  iron  and  steel.  It  was  also  observed 
that  the  pieces  of  iron  and  steel  which  were  rubbed  with 
this  ore  acquired  the  same  property.  This  strange  ore 
is -known  as  magnetite  and  probably  derived  its  name  from 
Magnesia,  a  province  of  Asia  Minor  in  which  the  ore  is 
quite  abundant.  The  ore  is  also  found  in  Norway,  Sweden, 
and  in  the  American  continent.  Pieces  of  ore  which 
possess  this  property  of  attraction  are  called  lode  stones 
or  natural  magnets.  Pieces  of  steel  which  have  acquired 
the  property  of  attracting  other  pieces  of  iron  and  steel, 
by  being  stroked  with  natural  magnets,  are  called  artificial 
magnets.  Artificial  magnets  may  also  be  made  by  pass- 
ing an  electric  current  around  bars  of  steel.  More  will 
be  said  about  this  method  later. 

Experiment  50.  —  Rub  a  knife  blade  or  small  piece  of  steel 
against  a  bar  magnet.  Now  bring  the  knife  blade  near  some  iron 
filings.  Has  it  acquired  the  power^to  attract  bits  of  iron?  What 
kind  of  magnet  is  it? 

Law  of  Magnetic  Poles.  —  If  iron  filings  are  sifted  over 
a  magnet,  it  will  be  observed  that  the  filings  cling  in  a 
large  bunch  at  each  end  of  the  magnet,  but  in  the  middle 
of  the  bar  scarcely  any  filings  will  cling.  These  centers 
of  attraction  are  called  the  poles  of  the  magnet.  The 

186 


MAGNETISM  AND  ELECTRICITY 


187 


end  that  points  north  when  the  magnet  is  free  to  turn 
is  called  the  north  pole  and  the  other  end  the  south  pole. 

Experiment  51. —  Suspend  a  bar  magnet  in  such  a  way  that  it 
is  free  to  move  (Figure  153)  and  determine  its  north  pole  and  south 
pole.  In  the  same  way  determine  the  poles  of  another  similar 
magnet.  Now  bring  the  North  (N)  Pole  of  the  first  magnet  near 
the  N  pole  of  the  second  and  note  the 
result.  Test  the  attraction  of  the  two 
South  (S)  Poles  for  each  other.  Now 
test  the  attraction  of  the  N  and  S  Poles 
for  each  other.  In  the  absence  of  bar 
magnets,  knitting  needles  may  be  mag-  A  N 
netized  and  used  in  the  above  experi-  ^ 
ment. 

From  this  experiment  the  law 
of  magnetic  poles  may  be  formu- 
lated :  Like  poles  repel  each  other 
and  unlike  poles  attract. 

Induced  Magnetism.  —  A  piece 
of  iron  becomes  a  magnet  by  in- 
duction when  it  touches  or  is 
brought  near  the  pole  of  a  magnet.  Suspend  a  nail  from 
the  end  of  a  strong  bar  magnet.  Another  nail  may  be 
suspended  from  the  first,  a  third  from  the  second,  and 
so  on.  Now  hold  the  first  nail  firmly  and  remove  the 
bar  magnet  by  sliding  so  that  the  nails  will  not  be  jarred. 
The  instant  that  the  bar  magnet  leaves  the  first  nail 
the  others  will  drop  apart,  showing  that  the  nails  were 
strong  magnets  only  so  long  as  they  were  in  contact  with 
the  bar  magnet. 

Experiment  52.  —  Magnetic  Fields.  —  Lay  a  bar  magnet  on 
the  table  and  cover  it  with  a  paper,  over  the  surface  of  which  fine 
iron  filings  are  strewn.  When  the  paper  is  gently  tapped,  the  filings 
will  arrange  themselves  in  lines  reaching  from  one  pole  to  the 


FIG.  153.  — Like  poles  of 
magnets  repel  each  other; 
unlike  poles  attract  each 
other. 


188 


GENERAL  SCIENCE 


other  (Figure  154).  These  lines  are  parallel  to  the  lines  of  force  of 
the  magnet  and  may  be  said  to  represent  them.  Blueprint  paper 
may  be  used  for  this  experiment,  and  if  held  in  the  sunlight  while 

the  filings  are  in  place,  will 
give  a  permanent  record  of 
their  position,  when  devel- 
oped. 

Perform  the  experiment 
using  two  magnets  with  like 
poles  near  each  other  (Figure 
155). 


FIG.  154.  —  Direction  of  the  Lines  of 
Force  Around  a  Bar  Magnet. 


The  magnetic  field  is 
the  region  about  a  magnet 
in  which  magnetic  forces 
can  be  detected.  The 

above  experiments  show  the  direction  of  these  forces 
at  every  point  in  the  plane  cut  by  the  sheet  of  paper. 
Each  little  particle  becomes  a  magnet  by  induction  and 
arranges  itself  so  that  it  lies  lengthwise  in  the  direction 
of  the  lines  of  force 
at  that  point. 

Nature  of  Magne- 
tism. —  Make  a  small 
magnet  by  rubbing  a 
small  piece  of  watch 
spring  on  a  bar  mag- 
net. Test  its  strength 
on  some  filings  or 
small  nails.  Heat  the 
piece  of  watch  spring 
and  again  test  its 
magnetism.  Make  another  such  magnet  and  hammer  it. 
Its  magnetism  will  be  found  to  be  much  diminished. 
Fill  a  small  test  tube  with  iron  filings  and  stroke  the 


FIG.  155.  —  Showing  the  Direction  of  the 
Lines  of  Force  when  the  Like  Poles  of  Two 
Magnets  are  Brought  Near  Each  Other. 


MAGNETISM  AND  ELECTRICITY 


189 


tube  with  a  magnet.     The  tube  of  filings  will  now  act  as  a 
single  magnet.    If  the  tube  is  shaken,  the  magnetism  is  lost. 


I   Sy  W          ^        -v  -w    —  N^          ^  ^  I 

FIG.  156.  —  When  the  molecules  of  a  bar  magnet  are  disarranged, 
the  bar  loses  its  magnetism. 

These  experiments  lead  to  the  conclusion  that  at  all 
times  every  molecule  in  a  piece  of  iron  or  steel  is  a  magnet, 
but  that  the  bar  as  a  whole  becomes  a  magnet  only  when 


FIG.  157.  —  The  Earth's  Agonic  and  Isogonic  Lines. 
Heavy  black  lines  are  agonic  lines ;  light  black,  isogonic  lines. 


190 


GENERAL  SCIENCE 


some  force  causes  the  molecules  to  arrange  themselves  in 
a  certain  order.  The  force  which  we  have  used  in  our 
experiments  is  simply  the  magnetic  force  in  other  mag- 
nets. After  the  molecules  in  a  bar  have  been  arranged 
so  that  the  bar  itself  acts  as  a  magnet,  any  force  which 
disarranges  the  molecules  will  cause  a  loss  of  magnetism 
in  the  bar  (Figure  156). 

Magnetic  Condition  of  the  Earth.  —  The  earth  is  a  great 
magnet  with  its  S  pole  somewhere  near  the  geographical 

north  pole  and  its  N  pole  near 
the  geographical  south  pole.  Dr. 
William  Gilbert  first  suggested 
that  the  earth  was  a  magnet  and 
offered  it  as  an  explanation  of 
the  behavior  of  the  compass.  All 
of  us  have  read  of  the  troubles 
of  Columbus  on  his  first  voyage, 
and  especially  those  due  to  the 
alarm  of  his  sailors  when  they 
discovered  that  the  compass  no 
longer  pointed  north.  The  reason 
for  the  variation  of  the  compass 
is  found  in  the  fact  that  the 
magnetic  poles  and  the  geo- 

FIG.  158.  — A  Dipping  Needle.  &,  .      ,  ,  .      .  , 

graphical  poles  do  not  coincide. 

The  number  of  degrees  which  the  needle  varies  from 
the  true  north  and  south  line  is  called  its  declination. 
There  are  not  many  places  where  the  needle  points 
exactly  north  or  where  the  declination  is  zero.  Lines 
passing  through  points  of  zero  declination  are  called 
agonic  lines  (Figure  157).  Lines  which  pass  through 
points  having  the  same  declination  are  called  isogonic 
lines. 


MAGNETISM  AND   ELECTRICITY 


191 


FIG.  159.  —  A  Homemade  Dipping 
Needle. 


The  Dipping  Needle.  —  Just  as  the  iron  filings  arranged 
themselves  so  that  they  were  lying  in  the  direction  of  the 
lines  of  magnetic  force  at  that  point,  so  a  compass  needle 
which  is  balanced  and  free  to  move  in  a  vertical  plane 
will  arrange  itself  parallel 
with  the  earth's  magnetic 
lines  of  force  at  that  place 
(Figure  158). 

Experiment  53 .  —  Pass  two 
unmagnetized  knitting  needles 
through  a  cork  near  the  center 
and  at  right  angles  to  each 
other  (Figure  159).  With  a  pin 
(a)  the  system  may  be  adjusted 
so  that  it  will  be  perfectly  bal- 
anced. Now  magnetize  the  neeble  b,  being  careful  not  to  change 
its  position  in  the  cork.  Replace  the  needle  on  the  supports  so  that 
the  N  pole  will  point  north.  Does  the  needle  balance  as  before? 

.      QUESTIONS 

1.  What  is  the  difference  between  permanent  magnetism  and 
induced  magnetism? 

2.  Name  four  ways  by  which  the  magnetism  of  a  magnet  may 
be  destroyed. 

3.  What  is  meant  by  the  magnetic  field? 

4.  How  would  an  explorer  know  when  he  had  reached  the 
north  or  south  magnetic  pole? 

5.  How  should  magnets  be  stored  in  the  laboratory  so  that  they 
will  not  lose  their  magnetism  so  rapidly? 

6.  Will  two  horseshoe  magnets  of  equal  strength  cling  to  each 
other?     Explain. 

7.  Why  does  soft  iron  lose  its  magnetism  so  quickly? 

Electrification  by  Friction.  —  If  a  stick  of  sealing  wax 
or  a  piece  of  hard  rubber  is  rubbed  with  a  woolen  cloth 
or  a  piece  of  cat's  fur,  it  will  attract  small  pieces  of  paper, 
pith  balls,  cork,  and  other  light  bodies.  A  glass  rod 


192  GENERAL  SCIENCE 

rubbed  with  a  piece  of  silk  also  acquires  this  power  of 
attraction.  It  is  thought  that  a  Greek  philosopher 
named  Thales  discovered  this  property  in  a  substance 
called  amber,  and  for  many  years  amber  was  supposed 
to  be  the  only  substance  possessing  this  property.  Since 
amber  in  common  with  a  few  metals  was  called  "  elec- 
tron "  by  the  Greeks,  Dr.  Gilbert  of  England  many 
years  later  gave  the  name  "  electric  "  to  these  phe- 
nomena. 

Place  some  bits  of  paper  under  a  pane  of  glass  which 
is  supported  by  two  books  (Figure  160).     Rub  the  upper 


FIG.  160. 

surface  of  the  glass  with  a  piece  of  silk  and  notice  how 
the  bits  of  paper  are  disturbed. 

Two  Kinds  of  Electricity.  -  -  The  electricity  which  is 
produced  upon  glass  by  rubbing  it  with  silk  is  called  posi- 
tive electricity  and  that  produced  upon  the  rubber  is 
called  negative  electricity.  Electricity  is  usually  pro- 
duced when  two  unlike  substances  are  rubbed  together, 
and  the  kind  may  be  determined  by  comparing  it  with 
that  formed  on  glass  or  rubber.  Thus  all  electrified 
bodies  which  act  with  respect  to  other  bodies  like  a  glass 
rod  rubbed  with  silk  are  said  to  be  positively  electrified, 
while  those  that  act  like  a  piece  of  hard  rubber  that  has 
been  rubbed  with  the  woolen  cloth  are  said  to  be  nega- 
tively electrified. 


MAGNETISM  AND  ELECTRICITY 


193 


Experiment  54.  —  Suspend  a  pith  ball  with  a  silk  thread  as 
shown  in  Figure  161.  When  an  electrified  glass  rod  is  brought 
near,  the  pith  ball  is  attracted  to  the  rod.  It  clings  to  the  rod  for 
a  moment  and  then  springs  away  from  it. 
The  ball  has  received  a  positive  charge  from 
the  positive  charged  rod.  Now  as  the  rod 
is  brought  near  the  ball  it  moves  away  as 
if  pushed  by  some  invisible  force.  Next  rub 
a  hard  rubber  or  ebonite  rod  with  flannel 
or  cart's  fur  and  bring  it  near  the  pith  ball. 
It  will  be  found  that  the  ball  is  no  longer 
repelled  as  with  the  glass  rod,  but  that  it  is 
strongly  attracted.  To  discharge  the  pith 
ball,  hold  it  in  the  finger  for  a  moment. 

Hang  two  pith  balls  from  the  same  point 
of  suspension  and  charge  both  balls  with 
the  same  kind  of  electricity.  The  balls  now 
repel  each  other  (Figure  162). 


FIG.  161.  — A  Pith  Ball 
Electroscope. 


It  is  evident  from  these  experiments 

that  electrical  charges  of  like  kind  repel 

each  other  and  charges  of  unlike  kind  attract  each  other. 

Conductors  and  Insulators.  —  A 
substance  which  conducts  or  trans- 
mits electricity  readily  is  called  a 
conductor,  while .  a  substance  that 
does  not  is  called  an  insulator,  or 
non-conductor.  All  metals  and  solu- 
tions of  salts  and  acids  in  water  are 
conductors  of  electricity,  while  glass, 
rubber,  shellac,  dry  air,  wood,  silk, 
and  oils  are  good  insulators.  When 
a  metal  rod  is  held  in  the  bare  hand 
and  rubbed  with  some  substance  such 
as  a  woolen  cloth,  a  charge  does  not 
FIG.  162.  appear  upon  the  rod,  because  the 


194  GENERAL  SCIENCE 

body  conducts  the  electricity  away  as  fast  as  it  is  made. 
With  non-conductors  such  as  glass,  the  charge  remains 
where  it  is  developed.  In  the  commercial  use  of  electricity 
both  conductors  and  insulators  are  of  great  value. 

Experiment  55.  —  Support  one  end  of  a  metal  rod  on  an  elec- 
troscope and  the  other  end  on  an  insulating  stand  (Figure  163). 
Bring  a  charged  body  near  the  end  of  the  rod.  The  divergence 

of  the  leaves  of  the 
electroscope  shows 
that  the  charge  has 
been  carried  by  the 
rod  to  the  electro- 
scope. The  rod  is 
a  conductor  of  elec- 
tricity. Test  the 
conductivity  of 
FIG.  163.  other  substances. 

Theory  of  Electricity.  —  To  study  the  theory  of  elec- 
tricity we  must  introduce  the  reader  to  a  new  and  very 
interesting  physical  character,  the  electron.  All  the 
atoms  of  all  substances  are  known  to  contain  both  posi- 
tive and  negative  electricity.  The  negative  electricity 
exists  in  the  form  of  electrons  or  particles  of  negative 
electricity.  The  positive  electricity  probably  exists  as 
the  center  or  nucleus  around  which  these  little  particles 
of  negative  electricity  are  grouped.  They  cling  together 
by  reason  of  having  opposite  or  unlike  charges,  the  posi- 
tive charge  just  equaling  the  sum  of  the  charges  of  the 
little  electrons.  We  are  most  concerned  with  these  nega- 
tive particles  or  electrons  at  present,  for  they  have  a 
very  important  part  in  our  everyday  life.  If  a  piece  of 
woolen  cloth  is  rubbed  on  a  piece  of  hard  rubber,  some 
of  these  electrons  are  brushed  from  their  places  on  the 
atoms  of  the  piece  of  cloth  and  collect  on  the  piece  of 


MAGNETISM  AND   ELECTRICITY  195 

rubber,  and  we  say  the  rubber  rod  has  a  negative  charge. 
We  simply  mean  that  some  of  the  electrons  which  belong 
on  the  cloth  have  been  removed  to  the  rod  and  that  for 
the  present  the  atoms  of  the  rubber  rod  are  overcrowded 
with  electrons.  Now,  since  the  electrons  are  little  par- 
ticles of  negative  electricity,  of  course  the  rod  will  ex- 
hibit a  negative  charge.  We  must  remember  that  the 
little  electrons  have  like  charges  and  repel  each  other ; 
so  whenever  we  have  this  overcrowding  of  electrons,  we 
find  them  pushing  each  other  in  all  directions  as  if  to 
make  their  condition  less  crowded.  In  fact,  if  any  other 
object  is  brought  near,  a  number  of  them  will  be  pushed 
over  on  it.  As  the  number  of  these  electrons  on  a  given 
insulated  area  is  increased,  the  crowding  becomes  so  great 
that  finally  they  are  forced  across  great  air  gaps  with  a 
disruptive  charge ;  as  is  the  case  when  an  electrical 
machine  is  operated  or  as  in  the  case  of  lightning. 

If  glass  is  rubbed  with  silk,  we  say  the  glass  receives  a 
positive  charge,  but  what  really  happens  is  that  the  elec- 
trons let  go  of  the  glass  rod  and  collect  on  the  silk.  There 
is  a  lack  of  negative  particles  on  the  glass,  and  we  say  it 
has  a  positive  charge. 

An  unelectrified  body  is  composed  of  atoms  in  which 
the  strength  of  the  charge  on  the  positive  nucleus  is 
exactly  counterbalanced  by  the  sum  of  the  negative 
charges  or  electrons. 

Charging  a  Body  by  Induction.  —  Suspend  two  egg- 
shells which  have  been  covered  with  tin  foil  by  silk 
threads,  so  that  they  touch  each  other  (Figure  164).  Bring 
a  positively  charged  rod  near  the  shell  A.  While  the 
rod  is  in  this  position  both  shells  will  be  electrified.  A 
will  have  a  negative  charge  and  B  a  positive  charge; 
the  reason  being  that  some  of  the  electrons  (negative 


196 


GENERAL  SCIENCE 


FIG.  164. 


particles  of  electricity)  of  the  shells  are  attracted  by  the 
positively  charged  rod,  thus  producing  an  excess  of  elec- 
trons on  A  and  a  lack  of  electrons  on  B.  If  the  rod  is 
taken  away,  the  electrons  which  have  been  drawn  to  A 

will  flow  back  to  their 
places  and  neither  shell 
will  show  any  charge. 
If,  however,  the  shells 
are  separated  while  the 
rod  is  near  the  shell  A, 
each  shell  will  be  per- 
manently electrified,  A 
having  a  negative 
charge  and  B  a  posi- 
tive charge.  The  charges  on  the  shells  may  be  tested  in 
the  usual  way. 

A  similar  experiment  may  be  performed  with  one  foil- 
covered  shell.  When  the  positively  charged  rod 
brought  near  one  end  of 
the  shell  (Figure  165),  the 
electrons  are  drawn  to 
that  end,  producing  a  lack 
of  electrons  at  the  other 
end.  Now  while  the  rod  is 
still  in  this  position,  touch 
the  opposite  end  with  the 
finger.  Electrons  will  flow 
from  the  finger  to  the 
shell  to  make  up  the  defi- 
ciency of  electrons  on  that  end.  When  the  rod  is  taken 
away,  the  shell  will  be  found  to  be  negatively  electrified. 
Charging  a  body  in  this  way  is  called  charging  by 
induction. 


is 


FIG.  165.  —  Electrons    are    drawn   toward 
the  positively  charged  glass  rod. 


MAGNETISM  AND  ELECTRICITY 


197 


Storing  a  Charge :  Condensers.  —  If  the  finger  or 
some  other  conductor  is  brought  near  a  charged  body, 
sparks  will  pass.  The  amount  of  the  charge  which  may 
be  stored  on  an  object  is  limited  by  the  size  and  shape 
of  the  object  and  its  proximity  to  conductors.  A  charge 
escapes  more  readily  from  points  than  from  evenly  curved 
surfaces.  Usually  before  the  charge  on  an  object  is  very 
great  it  escapes  by  way  of  the  air  or  some  other  conductor. 
A  greater  charge  can  be  stored  on  a  body  on  a  dry  day 
than  on  a  damp  day,  because  moisture  in  the  air  makes 
it  a  better  conductor  of  electricity.  To  store  a  large 
amount  of  electricity  on  an  object,  it  is  simply  necessary 
to  insulate  it  properly  and  bring  it  near  another  con- 
ductor which  is  attached  to  the  earth.  This  is  the  prin- 
ciple of  the  condenser. 

Experiment  56.  —  Place  some  tin  foil  on  both  sides  of  a  common 
windowpane  as  shown  in  Figure  166  and  connect  one  side  with  the 
earth.  Now  if  the  foil  on  the  side  A  be  connected  with  some  source 
of  positive  electricity,  electrons  will 
be  attracted  from  the  earth  to  plate 
B  in  sufficient  numbers  to  balance 
the  positive  charge  on  A.  A  very 
large  charge  thus  may  be  stored  on 
the  insulated  plates.  The  plates 
may  be  discharged  by  touching  the 
end  of  a  wire  to  one  side,  B,  and 
bringing  the  other  end  near  A. 

Explain  what  would  happen  if 
plate  A  be  connected  with  a  source 
of  negative  charges  instead  of  posi- 
tive charges.  FIG.  166. 

The  Leyden  Jar  was  one  of  the  first  forms  of  con- 
densers. It  was  first  used  in  1745.  It  consists  of  a 
glass  jar,  coated  inside  and  outside  to  about  two  thirds 


198 


GENERAL  SCIENCE 


FIG.  167.  —A  Leyden  Jar. 


of  its  height  with  tin  foil  (Figure  167).  The  inside  coating 
is  connected  by  a  chain  and  rod  to  a  knob,  and  the  out- 
side covering  is  connected  to  the  earth.  A  charge  may 

be  passed  by  way  of  the  knob 
and  rod  to  the  inside  coating 
of  the  jar,  the  action  being 
the  same  as  that  described 
above. 

The  Electrophorus.  —  The 
charges  which  we  are  able  to 
develop  on  glass  or  ebonite 
rods  are  small.  We  may  pro- 
duce larger  charges  by  taking 
advantage  of  the  principle  of  induction.  Figure  168  rep- 
resents a  sectional  view  of  the  electrophorus.  A  consists 
of  a  plate  of  ebonite  or  a  shallow  pan  filled  with  sealing 
wax  or  resin;  B  is  a  metal  disk  (tin  or  brass),  fastened 
to  an  insulating 
handle  of  ebonite 
or  glass.  Rub  the 
plate  A  with  some 
cat's  fur  or  woolen 
cloth.  Place  the 
metal  disk  B  on  the 
plate  and  touch  it 
with  the  finger  while 
it  is  in  this  position. 
Now  lift  the  disk 
and  test  its  charge. 
Lift  the  disk  with- 
out touching  it  and 
test  its  charge.  Lift 

the   disk   before   re-  FIG.  168.  —  The  Electrophorus. 


..-A 


'/////n/iiiiiiiiiiii/iiiiinnni 


\ 


MAGNETISM  AND   ELECTRICITY 


199 


moving  the  finger  from  the  disk  and  test  its  charge. 
What  kind  of  charge  should  be  on  the  disk?  What  kind 
of  charge  passes  through  the  body  to  the  earth  when  the 
finger  is  placed  on  the  disk? 

When  the  charged  disk  is 
brought  near  an  object,  a  spark 
will  pass  with  a  slight  cracking 
noise.  When  the  spark  passes, 
the  air  is  heated  and  its  sudden 
expansion  and  contraction  causes 
the  noise. 

Atmospheric  Electricity.  —  It 
was  Benjamin  Franklin  who  first 
demonstrated  that  lightning  is 
simply  a  great  spark  of  frictional 
electricity.  On  the  approach  of 
a  thunderstorm  he  sent  up  a  kite 
having  at  its  top  a  pointed  metal 
rod.  The  kite  string  was  insu- 
lated from  the  earth.  As  soon 
as  this  string  became  moistened 
by  the  rain  electric  sparks  were 
drawn  from  a  key  attached  to 
the  string.  These  sparks  proved 
to  be  the  same  as  those  obtained 
by  rubbing  a  glass  rod  with  silk 
(Figure  169). 

The  air  between  two  charged  clouds  or  between  a  cloud 
and  the  earth  acts  like  the  insulating  substance  in  a  con- 
denser. The  rapid  formation  of  raindrops  generates  large 
quantities  of  electricity  and  finally  the  charge  on  the 
cloud  becomes  so  great  that  it  bursts  through  the  inter- 
vening air  to  the  neighboring  cloud  or  to  the  earth. 


FIG.  169.  —  Franklin's  Experi- 
ment to  Test  the  Identity  of 
Lightning. 


200  GENERAL   SCIENCE 

QUESTIONS 

1.  Name  some  uses  of  insulators.     Of  conductors. 

2.  How  may  a  metal  rod  be  electrified? 

3.  Why  do  we  connect  the  outer  coating  of  a  Leyden  jar  to  the 
earth? 

4.  How  do  lightning  rods  protect  buildings?     Why  are  light- 
ning rods  pointed? 

'5.    Explain  how  the  "  electrophorus  "  is  charged. 

6.  What  do  we  mean  when  we  say  lightning  "  strikes  "? 

7.  Experiments  with  frictional  electricity  are  performed   more 
easily  on  dry  days.     Why? 

Current  Electricity.  —  If  a  wire  is  connected  with  the 
outer  coating  of  a  charged  Leyden  jar  and  then  brought 
near  the  knob  at  the  top,  a  spark  will  pass  and  the  two 
coatings  will  be  brought  to  the  same  electrical  potential. 
A  current  passes  through  the  wire,  but  only  for  a  very 
short  time.  About  the  beginning  of  the 
nineteenth  century  two  men,  Galvani  (1786) 
and  Volta  (1792),  working  independently, 
discovered  and  studied  a  method  of  main- 
taining a  constant  difference  of  electrical 
potential  between  two  substances  and  thus 
a  means  of  producing  a  continuous  electric 
current.  If  two  different  metals  such  as 
copper  and  zinc  are  placed  in  dilute  sul- 
FIG.  170.— A  Sim-  phuric  acid  and  connected  by  a  wire  (Figure 
pie  Voltaic  CeU.  J^Q^  a  continuous  current  of  electricity 
will  pass  from  the  copper  through  the  wire  to  the  zinc. 
Such  an  arrangement  is  called  a  voltaic  cell.  In  com- 
mercial cells  carbon  is  commonly  used  instead  of  copper. 
Kinds  of  Cells.  -  -  There  are  a  number  of  different 
kinds  of  cells,  but  in  every  case  they  depend  upon  chemi- 
cal action  of  some  sort.  In  the  voltaic  cell,  zinc  is  slowly 
decomposed  with  the  formation  of  hydrogen  and  zinc 


MAGNETISM  AND  ELECTRICITY  201 

sulphate  in  addition  to  the  current  produced.  This  form 
of  cell  is  of  little  practical  value,  however,  because  the 
little  bubbles  of  hydrogen  collect  in  such  numbers  on 
the  carbon  or  copper  that  they  weaken  and  finally  stop 
the  passage  of  the  current.  A  cell  in  such  a  condition  is 
said  to  be  polarized*  If  bichromate  of  potassium  is  dis- 
solved in  the  sulphuric  acid,  it  will  unite  with  the  hydrogen 
as  fast. as  it  forms  at  the  zinc  and  thus  prevent  it  from 
reaching  the  carbon  or  copper  and  stopping  the  current. 

Another  form  of  celt  in  which  polarization  is  com- 
pletely avoided  is  the  gravity  or  crowfoot  type  of  the 
Daniell  cell.  This  cell  is  commonly 
used  on  telegraph  lines.  A  group  of 
copper  plates  is  placed  in  the  bottom 
of  the  jar  and  surrounded  with  crys- 
tals of  copper  sulphate  (Figure  171). 
A  zinc  plate  is  hung  near  the  top, 
and  the  jar  is  then  filled  with  a  very 
dilute  solution  of  sulphuric  acid. 
Hydrogen  is  formed  at  the  zinc  plate, 
but  on  its  way  to  the  copper  it  is  FlG-  m- 

used  up,  and  copper  from  the  copper  sulphate  is  deposited 
on  the  copper  plate  in  its  stead.  The  copper  sulphate 
solution,  being  heavier  than  the  acid  solution,  remains 
near  the  bottom  of  the  jar. 

One  of  the  most  common  and  convenient  types  of  cells 
is  the  dry  cell.  In  this  cell  the  zinc  serves  a  double  pur- 
pose. It  forms  one  plate  of  the  cell  and  also  is  the  con- 
tainer for  the  chemicals  which  fill  the  space  between  the 
carbon  center  and  the  zinc.  These  chemicals  are  sal 
ammoniac,  manganese  dioxide,  and  charcoal,  mixed  with 
water  enough  to  make  a  paste.  The  cell  is  sealed  to  pre- 
vent the  evaporation  of  the  water. 


202  GENERAL  SCIENCE 

Effects  of  Electric  Currents  :  Heating  Effects.  —  Con- 
nect two  or  three  dry  cells  in  series  with  a  short  piece  of 
fine  iron  or  German  silver  wire.  The  wire  will  become 
red  hot  and  may  be  burned.  Try  this  experiment  with 
different  lengths  of  fine  iron  and  copper  wire  with  differ- 
ent-sized batteries. 

A  current  in  passing  through  a  wire  must  overcome 
the  resistance  of  the  wire.     This  resistance  differs  with 
the  kind  of  material  of  which  the  wire  is  made,  the  size 
of  the  wire,  and  its  length.     Some  sub- 
stances are  much  better  conductors  of 
an  electric  current   than  others.     For 
example,  copper  is  a  better  conductor 
than  iron,  and  silver  is  a  slightly  better 
conductor  than   copper.     For  a  given 
kind  of  material  the  resistance  varies 
with  the  size  and  length  of  the  wire. 
The  smaller  the  wire  the  greater  the 
FIG  172  —  ACommer-  resistance,  and  the  longer  the  wire  of  a 
ciai  Tungsten  Lamp,     given  size  the  greater  the  resistance. 

Table  of  Resistances  of  a  Few  Common  Metals 

Silver      .     .     1.00     Iron      ,,     .     .     6.00     German  silver  .     15.00 
Copper    .     .     1.11     Platinum   .     .     7.20     Spring  steel      .     13.5 

German  silver  wire  is  commonly  used  in  electric 
heaters,  electric  toasters,  electric  stoves,  electric  flat- 
irons,  and  similar  appliances.  The  size  of  the  wire  is 
carefully  graded  for  the  current  on  which  it  is  to  be 
used  in  order  that  the  temperature  will  be  right  for  the 
different  uses. 

Electric  Lighting.  -  -  The  same  principle  as  that  in- 
volved in  electric  heating  is  involved  in  the  electric  light 
bulb.  A  fine  wire  or  filament  of  carbon  is  inclosed  in  a 


MAGNETISM   AND  ELECTRICITY 


203 


bulb  from  which  air  has  been  almost  exhausted.     When 

the  current  passes  through  the  filament,  it  is  heated  to 

the  point  of  incandescence.     It  does 

not  burn  because  of  lack  of  oxygen 

(Figure  172). 
At  the  present  time  tungsten  and 

tantalum  filaments  have  largely  re- 
placed the  carbon 
for  use  in  incandes- 
cent lamps,  since 
they  are  nearly  three 
times  as  efficient  as 
the  carbon  lamps. 

The  electric 
"  arc  "  light  is  pro- 
duced by  placing 
two  carbon  rods  end 
to  end  in  a  strong 

electric  current.  If  the  carbons  are  sepa- 
rated slightly  after  the  ends  are  heated 
red  hot,  the  current  will  continue  to  flow. 
The  conducting  layer  of  incandescent 
vapor  between  the  ends  of  the  carbon  is 
called  the  electric  arc  (Figures  173-174). 
The  temperature  in  this  arc  is  the  hottest 
that  man  has  been  able  to  produce.  It 
will  vaporize  all  known  substances. 
When  the  electric  arc  is  inclosed  in  a  box 

FIG.  174.— TheEiec-  (Figure  175)  made  of  high  heat-resisting 
trie  Arc  Lamp.  materials,  it  is  called  an  electric  furnace. 
Magnetic  Effects  of  Currents.  —  If  we  hold  a  wire 

carrying  a  current  near  a  compass,  the  needle  will  be 

deflected.     If  the  current  is  moving  from  south  to  north 


FIG.  173.  — The  Electric 
Arc. 


204 


GENERAL  SCIENCE 


in  a  wire  held  directly  over  the  compass,  the  AT  pole  of 
the  needle  will  move  to  the  west  (Figure  176).  If  the  wire 
is  held  under  the  compass,  the  N  pole  will  move  to  the 

east.  If  the  current 
is  reversed,  the  direc- 
tion of  the  needle  will 
be  reversed. 

Pass  a  wire  carrying 
a  current  through  a 
sheet  of  cardboard 
which  is  held  in  a  horizontal  position  (Figure  177).  With 
the  aid  of  a  compass  test  the  magnetic  field  about  the 
wire.  As  the  compass  is  moved  it  will  be  found  that 
the  position  of  the  needle  changes  in  such  a  way  as  to 
form  a  right  angle  with  a  line  drawn  from  the 'wire  to 
the  middle  of  the  needle.  The  needle  of  the  compass 


FIG.  175.  —  An  Electric  Furnace. 


FIG.  176.  —  Effect  of  Electric  Cur- 
rent on  Magnetic  Needle. 


FIG.   177. 


will  be  tangent  to  a  circle  drawn  through  that  point 
with  the  wire  as  the  center  of  the  circle. 

From  these  experiments  it  will  readily  be  seen  that  a 
wire  carrying  a  current  is  surrounded  by  a  magnetic  field. 
The  magnetic  lines  of  this  field  lie  in  circles  about  the 
wire  in  such  a  way  that  if  the  wire  is  grasped  with  the 


A  Lifting  Magnet  Lifting  a  Large  Casting. 


MAGNETISM  AND   ELECTRICITY 


205 


right  hand  so  that  the  thumb  points  in  the  direction  in 
which  the  current  is  flowing,  the  fingers  will  encircle  the 
wire  in  the  same  direction  as  do  the  magnetic  lines. 

The  Electromagnet.  - 
The  magnetic  effect  of  an 
electric  current  is  of  great 
practical  value  in  its  many 
applications.  We  have 
learned  that  a  wire  carry- 
ing a  current  is  sur- 
rounded by  a  magnetic 
field,  and  we  should  ex-  FlG  178._If  the  helix  is  free  to  turni 

pect     that    if    We    have    a    ^  w^  arrange  itself  in  a  north  and  south 
,  ....  .  position. 

number  of  wires  in  a  given 

space,  all  carrying  currents  in  the  same  direction,  the 
magnetic  field  would  be  strengthened.  The  same  effect 
may  be  obtained  by  winding  a  single  wire  in  the  form  of 
a  helix  (Figure  178).  The  wire  should  be  insulated  to 
avoid  the  short-circuiting  of  some  of 
the  turns  should  they  come  in  contact 
with  each  other.  If  this  helix  is  free 
to  turn,  it  will  behave,  like  a  mag- 
netic needle  in  taking  a  north  and 
south  position.  A  bar  of  soft  iron 
placed  in  the  coil  becomes  a  tempo- 
rary magnet.  Such  a  magnet  is  called 

FIG.  179.  — An  Electro-  _. 

magnet  of  the  Horseshoe  an  electromagnet.     The  greater  the 
number  of  turns  of  the  wire  in  the 
coil  the  stronger  will  be  the   magnetic   field   and  conse- 
quently the  stronger  will  be  the  electromagnet. 

Experiment  57.  —  Make  an  electromagnet  by  winding  a  bar  of 
soft  iron  in  the  shape  of  a  horseshoe  with  insulated  wire  (Figure 
179)  and  test  its  lifting  power. 


•'iiiiiiii 


206 


GENERAL  SCIENCE 


The  electromagnet  is  used  in  electric  bells,  telegraph 
instruments,  the  electric  crane,  and  many  other  appliances. 

The  Electric  Bell.  —  A  sim- 
ple application  of  the  elec- 
tromagnet is  the  electric  bell 
(Figure  180) .  When  the  elec- 
tric circuit  is  closed  at  A, 
the  current  flows  through  the 
coils  of  the  electromagnet  F. 
The  magnet  attracts  the 
hammer  or  armature,  causing 
it  to  strike  the  bell.  At  the 
same  time  the  circuit  is  broken 

DiaBrer  °f  the  El6CtriC    at  G  and  the  magnet  is  de- 
magnetized.    The  hammer  is 

thrown  back  by  the  spring  which  supports  it.  This 
closes  the  circuit  again  and  the  operation  is  repeated. 
So  rapidly  does  this  opening  and  closing  of  the  circuit 
take  place  that  if  the  bell  is  removed,  the  hammer  will 
produce  a  buzzing 
noise. 

The    Telegraph.  - 
In    this    instrument, 
which  is  another  ap- 
plication of  the  elec- 


FIG.   180. 


FIG.  181.  —  Diagram  of  Telegraph  Circuit. 


tromagnet,  the  earth 
is  used  instead  of  a 
second  wire.  When  the  key  K  (Figure  181)  is  closed, 
the  circuit  is  complete,  and  the  electromagnet  A  attracts 
the  sounder  B  and  holds  it  as  long  as  the  key  is  closed. 
When  the  circuit  is  broken  at  K,  the  sounder  is  pulled 
away  from  the  magnet  by  a  spring  at  C.  A  short 
closing  of  the  key  is  called  a  dot,  a  longer  time  a  dash. 


MAGNETISM  AND   ELECTRICITY  207 

Telegraph  operators  have  learned  to  read  these  messages 
by  interpreting  the  clicks,  representing  the  dots  and 
dashes  as  letters  of  the  alphabet. 

The  Telephone.  —  In  1875  Alexander  Graham  Bell 
demonstrated  to  the  world  that  the  sound  of  a  human 
voice  could  be  transmitted  by  electricity.  He  invented 
what  we  still  use  and  know  as  the  Bell  receiver.  The 
essential  parts  of  this  receiver  are  a  permanent  magnet 
wound  with  fine  wire  and  a  disk  of  thin  sheet  iron  held 
in  place  by  a  hard  rubber  case.  Figure  182  shows  a  simple 
arrangement  of  the  telephone  parts  and  how  they  work. 
At  each  end  of  the  line  is  a  bar  magnet,  surrounded  by 

Receiver  Receiver 


FIG.  182.  —  Telephone  System  and  Battery  Circuit. 

a  coil  of  fine  wire  and  a  thin  iron  disk.  The  disk  A  is 
set  in  vibration  by  the  sound  waves  whenever  such  waves? 
are  produced  in  front  of  it.  As  A  moves  back  and  forth 
in  the  magnetic  field,  currents  are  induced  in  the  coil  B. 
These  currents  are  transmitted  to  the  similar  coil  B'  at 
the  other  end  of  the  line  and  there  produce  changes  in 
the  magnetic  field  similar  to  the  changes  that  produced 
the  current  at  B,  The  disk  A'  is  set  in  motion  and 
vibrates  in  exactly  the  same  way  as  A,  with  the  result 
that  the  sounds  which  caused  the  vibration  at  A  are  re- 
produced at  A'. 

The  modern  telephone  uses  a  transmitter  and  a  re- 
ceiver, and  also  a  second  wire  as  shown  in  the  above 
diagram.  This  second  wire  is  necessary  because  of  the 


208  GENERAL  SCIENCE 

noise  and  numerous  electrical  disturbances  due  to  the 
many  uses  to  which  electricity  is  put  in  the  modern 
city. 

Chemical  Effects  —  Electrolysis.  —  In  the  chapter  on 
water  we  used  the  electric  current  to  separate  water  into 
the  two  gases  of  which  it  is  composed.  In  this  experi- 
ment the  gas  was  formed  at  each  terminal,  but  it  was 
formed  at  the  terminal  at  which  the  current  left  the 
liquid  twice  as  fast  as  at  the  other  terminal.  The  larger 
volume  of  gas  was  hydrogen  and  the  smaller  volume 
oxygen.  Solutions  of  a  number  of  compounds  may  be 
decomposed  in  this  way. 

Electroplating.  —  If  the  current  is  passed  through  a 
solution  of  copper  sulphate  instead  of  a  solution  of  sul- 
phuric acid,  the  ac- 
tion is  the  same  with 
the  exception  that  the 
copper  is  deposited  at 
the  negative  pole  in- 
stead of  hydrogen. 

FIG.  183.  —  An  Electroplating  Bath.  Tf.    .-,  ...  i 

If  the  positive  pole  is 

made  of  copper,  it  slowly  wastes  away  and  is  deposited 
on  the  other  pole.  This  is  the  method  used  in  com- 
mercial electroplating.  The  positive  pole  is  made  of 
the  material  with  which  the  other  pole  is  to  be  plated. 
In  Figure  183  the  positive  pole  (anode)  is  pure  silver, 
while  the  negative  pole  (cathode)  is  the  spoon  to  be 
plated.  These  are  both  placed  in  a  solution  of  a  silver 
compound.  When  the  current  passes,  silver  is  deposited 
on  the  spoon. 

The  Dynamo.  — We  learned  that,  when  a  bar  of  iron 
was  put  in  the  magnetic  field  of  a  coil  carrying  a  current, 
the  bar  was  magnetized.  The  reverse  of  this  is  also 


MAGNETISM  AND   ELECTRICITY 


209 


true.     When  the  magnet  is  placed  in  or  removed  from  a 
coil  of  wire,  a  current  is  produced  in  the  wire. 

Experiment  58.  —  Connect  a  coil  of  several  hundred  turns  of 
insulated  wire  with  a  galvanometer  (Figure  184).  Now  bring  the 
pole  of  a  bar  or  horseshoe  magnet  suddenly  into  the  coil  and  notice 
the  deflection  of  the 
pointer  of  the  galvanom- 
eter. When  the  pointer 
comes  to  rest,  remove 
the  magnet  quickly ;  the 
pointer  will  again  be  de- 
flected, but  in  the  op- 
posite direction. 

Experiments     will 
show  that  it  makes 


FIG.  184.  —  When  the  permanent  magnet  is 
placed  in  the  coil  a  current  of  electricity  is  in- 
duced in  the  coil  as  is  shown  by  the  deflection 
of  the  galvanometer  needle. 


no  difference  whether 
the  coil  be  held  sta- 
tionary and  the  magnet  placed  in  it,  or  the  magnet  held 
stationary  and  the  coil  moved  over  it.  The  current  in 
the  coil  of  wire  is  made  when  it  moves  through  a  mag- 
netic field.  This  is  the  principle  of  the  dynamo  (Figure 

185).  A  dynamo  consists  of  a 
coil  of  wire  revolving  in  a  mag- 
netic field.  The  magnet  may 
be  a  permanent  magnet  or  an 
electromagnet.  In  the  com- 
mercial instrument  the  arma- 
ture is  usually  made  up  of  a 
large  number  of  separate  coils 
ynamo'  of  insulated  wire.  The  dynamo 
is  used  to  produce  electricity  wherever  it  is  used  in  very 
large  quantities.  Through  its  agency  almost  any  kind  of 
power  may  be  changed  to  electric  power  (Figure  186). 
The  Falls  of  Niagara  furnish  power  to  run  many  dynamos 


FIG.  186.  —  A  Gasoline  Engine  Operating  a 
Westinghouse  Generator. 


FIG.  187.  —  A  5000-Horse  Power  Generator  and  Governor. 
210 


MAGNETISM    AND    ELECTRICITY  211 

whose  electricity  is,  in  turn,  used  for  lighting,  for  propelling 
street  cars,  for  heating,  for  factory  fcower,  and  in  various 
other  ways.  Electricity  may  be  cheaply  made  by  water 
power  and  conducted  great  distances  by  wires  to  cities 
and  mills  where  it  is  needed  (Figure  187) . 

Electric  Motors.  -  -  The  appearance  of  the  electric 
motor  is  similar  to  that  of  the  dynamo,  but  its  action  is 
reversed.  We  revolve  the  armature  of  a  dynamo  in  a 
magnetic  field  to  produce  a  current,  but  in  the  electric 
motor  the  current  is  passed  through  coils  of  the  armature, 
causing  it  to  revolve.  The  dynamo  is  a  machine  for 
producing  electric  current,  while  the  motor  is  a  machine 
for  utilizing  electric  current  and  may  be  used  to  run 
machinery  wherever  power  is  needed. 

QUESTIONS 

1.  Explain  how  polarization  stops  the  current. 

2.  Why  are  gravity  cells  called  by  that  name? 

3.  Why  is  copper  used  in  electric  wiring? 

4.  What  do  we  mean  by  "  earthing  "  a  wire? 

5.  Name  four  uses  of  the  electromagnet. 

6.  Draw  a  diagram  of  an  electric  bell,  showing  how  it  works. 

7.  Why  do  we  use  soft  iron  in  an  electromagnet? 

8.  Why  are  fuse  plugs  used  on  electric  circuits? 

9.  How  does  a  current  given  by  a  cell  differ  from  that  given 
by  a  Leyden  jar? 

10.    Learn  how  to  make  a  sal  ammoniac  cell. 


CHAPTER   XII 
SOUND 

What  Causes  Sound.  —  When  the  string  of  a  guitar 
is  plucked,  it  gives  forth  a  continuous  sound.  If  a  light 
piece  of  metal  is  held  near  the  string,  it  will  be  struck  a 
number  of  tiny  blows  by  the  string  in  its  movements. 

Experiment  59.  —  Attach  a  pith  ball  or  a  light 
glass  ball  to  a  string  and  hold  it  near  a  tuning  fork 
that  has  just  been  struck  (Figure  188).  The  ball  is 
set  in  motion  by  the  vibration  of  the  fork. 

If  we  hold  a  piece  of  metal  near  a  large  bell 
that  has  just  been  struck,  we  find  that  the 
metal  in  the  bell  is  in  violent  vibration.  In 
short  we  find  that  where  a  sound  is  pro- 
duced, matter  has  been  set  in  motion.  It 
FIG.  188.  may  be  the  falling  of  a  tree,  the  collision  of 
two  bodies,  the  firing  of  a  shot,  or  the  blowing  of  a  whistle  ; 
but  an  examination  will  show  in  every  case  that  vibrat- 
ing matter  of  some  sort  has  caused  the 
sound.  •.,« 

Experiment  60.  —  Sound  Waves. — Suspend 
a  small  electric  bell  in  the  receiver  of  a  vacuum 
pump  (Figure  189).  If  we  set  the  bell  to  ring- 
ing and  pump  out  the  air,  we  find  that  the 
sound  becomes  fainter  as  the  vacuum  becomes 
greater.  Now  admit  the  air  slowly  and  note  the 
increase  in  sound.  FIG.  189. 

From  this  experiment  it  will  seem  a  logical  conclusion 
that  sound  will  not  pass  through  a  vacuum  and  that  air 

212 


SOUND  213 

carries  sound  to  the  ears.  This  is  correct ;  but  air  is  not 
the  only  substance  that  will  carry  sound.  Solids,  liquids, 
and  other  gases  will  also  carry  sound.  If  the  ear  is  held 
near  the  steel  rails  of  a  railroad,  a  train  approaching  at 
considerable  distance  may  be  heard.  It  is  also  quite  a 
familiar  fact  that  if  the  ear  is  held  under  water,  the  noise 
made  by  hitting  two  stones  together  some  distance  away 
may  be  heard  distinctly.  The  speed  of  sound  in  air  at 
0°  C.  is  1087  feet  a  second.  In  water  the  speed  is  about 
4600  feet  a  second  and  in  iron  16,700  feet.  The  speed  of 
sound  in  air  increases  with  the  temperature. 

When  two  boards  are  brought  together  suddenly,  air 
is  driven  from  between  them  with  considerable  force  and 
the  surrounding  air  is  pushed  back  in  all  directions.  This 
motion  is  communicated  to  the  next  layer  of  air  and  to 
succeeding  layers  as  wave  motion.  As  the  wave  moves 
farther  and  farther  from  its  source,  a  larger  volume  of 
air  is  affected  and  the  intensity  of  the  wave  decreases. 
If  an  ear  is  within  the  range  of  these  waves,  the  sensa- 
tion of  sound  is  produced.  Sounds  may  be  heard  in  all 
directions,  which  is  evidence  that  the  wave  advances  in 
the  form  of  the  surface  of  a  sphere. 

When  a  stone  is  dropped  in  still  water,  waves  are  pro- 
duced. These  waves  move  in  circles  outward  from  the 
source.  That  the  water  in  these  waves  does  not  move 
out  with  the  wave  may  be  proved  by  scattering  some 
light  material  on  the  surface  of  the  water.  Sound  waves 
are  similar  to  water  waves.  Water  waves  advance  as 
the  circumference  of  a  circle,  while  sound  waves  in  the 
air  advance  in  the  form  of  the  surface  of  a  sphere.  In 
such  a  wave  the  air  does  not  actually  move  forward. 
Air  is  very  elastic.  When  an  impulse  is  given  to  the  air  by 
some  sound-producing  source,  the  adjacent  layer  of  air  is 


214 


GENERAL  SCIENCE 


FIG.  190.  —  Diagram  Illustrating  the  Way 
Sound  Travels. 


compressed.     As  it  expands  it  compresses  a  second  layer 
and  so  on,  so  that  the  volume  of  the  air  affected  is  made 

up  of  layers  of  com- 
pressed and  rarefied 
air  (Figure  190). 

Waves  pass  over 
fields  of  standing 
grain ;  but  the  grain 
simply  bends  under 
the  pressure  of  the  wind  and  rises  again.  Wave  motion 
may  be  shown  by  the  following  experiment. 

Experiment  61.  —  Attach  one  end  of  a  small  rope  about  25  feet 
long  to  some  solid  object  such  as  the  wall.  Hold  the  other  end  of 
the  rope  in  the  hand  and  cause  waves  to  run  along  it  by  quick 
movements  of  the  hand.  The  waves  pass  from  one  end  of  the 
rope  to  the  other,  but  the  particles  of  the  rope  do  not  move 
forward. 

Echoes  are  due  to  the  reflection  of  sound.  When  we 
speak,  the  sound  waves  often  strike  some  reflecting  sur- 
face and  are  returned  to  the  source.  If  the  reflecting  sur- 
face is  near,  as  in  the  case  of  the  walls  of  a  small  room, 
the  echo  will  not  be  noticed ;  but  in  large  halls  the  echoes 
may  be  so  strong  as  seriously  to  inconvenience  a  speaker. 
Such  effects  may  be  remedied  by  substituting  light,  porous 
materials  for  the  hard  surfaces  of  reflecting  walls  and  by 
hanging  curtains  in  certain  parts  of  the  hall  to  destroy 
returning  sound  waves.  In  hilly  districts  echoes  are 
sometimes  heard  several  seconds  after  the  original  sound. 

Musical  Tones  and  Noises.  -  -  The  human  ear  quite 
readily  distinguishes  between  pleasing  sounds  and  those 
that  are  not.  Pleasing  sounds  are  musical  and  are  pro- 
duced when  the  vibrations  of  a  sounding  body  follow  each 
other  at  precisely  equal  intervals  of  time.  If  the  vibra- 


SOUND  215 

tions  do  not  follow  each  other  in  equal  intervals  of  time, 
the  result  is  noise. 

Pitch.  —  If  the  vibrations  which  produce  tones  were 
all  of  the  same  frequency,  music  would  be  impossible, 
since  we  would  have  but  one  tone.  Happily  this  is  not 
the  case.  As  the  number  of  vibrations  in  a  second  in- 
creases, the  tone  becomes  higher.  By  pitch  we  mean 
the  highness  or  lowness  of  a  sound.  Middle  C  on  the 
piano  is  produced  by  a  string  vibrating  256  times  a 
second.  Any  other  string  vibrating  the  same  number  of 
times  a  second  will  produce  a  tone  of  the  same  pitch.  If 
the  number  of  vibrations  a  second  be  doubled,  the  result 
will  be  another  C  an  octave  higher ;  and  if  the  number  be 
decreased  to  128  a  second,  the  result  is  C  an  octave  lower 
than  middle  C. 

Vibrating  Strings.  —  A  large  number  of  musical  in- 
struments employ  vibrating  strings  or  wires.  Variations 
in  pitch  are  obtained  by  varying  the  length,  tension,  and 


FIG.  191.  —  A  Sonometer. 

mass  of  the  strings.  For  example,  if  a  string  20  inches 
long  produces  a  tone  of  a  certain  pitch,  the  pitch  will  be 
an  octave  higher  if  the  length  of  the  string  be  changed 
to  10  inches.  The  shorter  the  string  the  higher  the  pitch. 
Or  we  may  say  the  vibration  frequencies  of  strings  are 
inversely  proportional  to  their  length. 

If  we  increase  the  tension  on  a  string,  the  pitch  will  be 
higher ;  and  if  we  decrease  the  size  of  the  string  and  keep 


216  GENERAL  SCIENCE 

the  length  and  tension  the  same,  the  pitch  will  be  higher. 
The  wires  of  a  piano  show  the  application  of  these  laws 
of  strings.  They  vary  from  strings  of  small  diameter 
and  a  few  inches  in  length  to  quite  large  strings  several 
feet  in  length.  The  high  notes  are  made  by  the  short 
strings,  the  low  ones  by  the  long  strings.  Test  the  truth 
of  these  statements  by  experiments  with  a  sonometer. 
(Fig.  191.) 

The  Voice.  —  The  larynx  or  voice  is  just  below  the 
throat  or  pharynx  at  the  top  of  the  trachea.  It  is  com- 
posed of  cartilages  bound  together  by  ligaments  and 
surrounding  muscles.  In  the  larynx  are  the  vocal  cords, 
which  are  the  chief  organs  of  the  voice.  These  cords  are 
folds  of  connective  tissue  placed  in  such  a  way  that  they 
may  be  stretched  at  will  across  the  opening.  The  pas- 
sage of  air  causes  them  to  vibrate,  and  sounds  are  pro- 
duced. 

If  we  cut  a  small  slit  in  a  piece  of  sheet  rubber  and  tie 
it  over  one  end  of  a  tube,  we  will  have  a  mechanism  sim- 
ilar to  that  which  produces  voice.  When  we  blow  through 
the  tube,  a  sound  is  produced  which  will  become  higher  in 
pitch  as  the  tension  on  the  rubber  is  increased.  Many 
animals  have  voice,  but  man  alone  possesses  the  power 
to  express  his  thoughts  in  articulate  sounds  or  speech. 

The  Hearing.  —  Sound  is  transmitted  from  a  vibrating 
object  to  the  ear  by  waves  in  the  air.  The  .ear  is  the 
organ  of  hearing.  For  convenience  in  description  it  is 
divided  into  three  parts,  the  external  ear,  the  middle  ear, 
and  the  inner  ear.  (Figure  192.) 

The  external  ear  is  an  irregularly  folded  cartilage  cov- 
ered with  skin.  Its  shape  is  especially  well  adapted  for 
catching  sound  waves  and  directing  them  through  the 
auditory  canal  to  the  middle  ear.  At  the  inner  end  of  the 


SOUND 


217 


auditory  canal  is  a  thin  layer  of  very  flexible  skin,  the 
tympanic  membrane,  which  also  forms  the  external  cover- 
ing of  the  middle  ear. 

The  middle  ear  is  a  small  cavity  lined  with  mucous 
membrane  and  connected  with  the  pharynx  by  the 
Eustachian  tube.  It  contains  a  chain  of  three  .bones 
named  from  their  shapes  the  hammer  (malleus) ,  the  anvil 


""*  Bone 


FIG.  192.  —  The  Human  Ear  Shown  in  Section.  Co,  Cochlea  (location  of 
real  hearing  organ)  ;  E.b,  Ear  Bones  ;  Eu,  Eustachian  Tube  ;  Ty.m,  Tympanic 
Membrane. 

(incus),  and  the  stirrup  (stapes)  (Figure  193).  These  bones 
extend  from  the  tympanic  membrane  to  the  membrane 
which  closes  the  opening,  fenestra  ovalis,  into  the  inner  ear. 
The  inner  ear  is  located  in  an  irregular  cavity  in  the 
temporal  bone.  Its  essential  part  is  composed  of  a 
membranous  sac  which  is  filled  with  a  liquid  called 
endolymph.  In  this  liquid  are  tiny  stones,  otoliths.  The 
first  part  of  the  inner  ear  is  called  the  vestibule.  To  the 
vestibule  on  one  side  is  attached  the  cochlea  in  which 


218 


GENERAL  SCIENCE 


ttalleus 


Stapes 


the  fibers  of  the  auditory  nerve  terminate  and  where  the 
auditory  impulses  originate.  To  the  other  side  of  the 
vestibule  the  three  semicircular  canals  are  attached. 
incus  These  canals  seem  to  have 

something  to  do  with  bal- 
ancing the  body. 

How  We  Hear.  — When 
a  vibrating  body  produces 
sound  waves  which  reach 
the  ear,  the  sensation  of 
sound  is  produced.  As  the 
waves  reach  the  ear  they 
are  collected  by  the  ex- 
ternal ear  and  concen- 
trated upon  the  tympanic 
membrane,  which  is  thus 
set  into  sympathetic  vi- 
bration with  the  object  which  caused  the  waves.  This 
vibration  is  communicated  through  the  bones  of  the 
middle  ear  to  the  liquids  of  the  inner  ear.  These  liquids 
distribute  the  vibrations  to  all  parts  of  the  inner  ear  and 
finally  to  the  fibers  of  the  auditory  nerve  (fibers  of  Corti) 
which  originate  the  proper  impulses  to  be  conveyed  to 
the  brain  as  sound  sensations. 


Tympanic  flembrane 
FIG.  193.  — The  Ear  Bones. 


QUESTIONS 

1.  What  is  meant  by  wave  length? 

2.  If  the  speed  of  sound  increases  two  feet  for  each   degree 
Centigrade,  what  will  be  the  speed  at  23°  C.  ? 

3.  If  the  velocity  of  sound  on  a  certain  day  is  1120  feet  per 
second  and  a  sounding  body  makes  560  vibrations  per  second, 
what  is  the  wave  length? 

4.  Three  seconds  elapse  between  a  flash  of  lightning  and  its 
attendant  thunder.     How  far  away  was  the  lightning? 


SOUND  219 

5.  What  is  the  form  of  a  sound  wave? 

6.  Two  strings  have  the  same  length  and  tension,  but  one  is 
larger  than  the  other.     In  what  respect  will  their  tones  differ? 

7.  Can  we  hear  sounds  farther  on  a  foggy  or  a  clear  day? 

8.  What  is  meant  by  "  pitch  "  of  sound?     By  quality? 

9.  Why  does  a  cold  sometimes  cause  deafness? 

10.  What  is  the  function  of  the  ear  wax? 

11.  What  is  sound? 

12.  Why  should  a  drum  head  be  well  stretched? 


CHAPTER  XIII 
LIGHT 

Light  and  its  Properties.  —  We  have  just  learned  that 
sound  waves  are  caused  by  the  vibrations  of  the  material 
bodies  about  us,  and  we  are  now  to  learn  that  light  is  due 
to  waves  produced  in  a  similar  way.  Light  waves  are 
not  waves  in  the  air,  but  in  the  ether,  a  medium  which 
fills  all  space  but  which  possesses  few  of  the  properties 
of  ordinary  matter.  These  waves  in  the  ether  are  pro- 
duced by  the  vibrations  of  the  same  little  electrons  which 
produce  the  charges  of  electricity.  '. 

While  studying  sound  we  learned  that  the  rate  of 
vibration  of  the  shorter  and  smaller  strings  was  much 
greater  than  the  rate  of  vibration  of  the  longer  and  larger 
ones.  The  electron  is  very  much  smaller  than  the  small- 
est string,  and  its  rate  of  vibration  is  very  much  greater. 

Heat  and  light  are  very  closely  associated.  Not  all 
hot  objects  give  off  light ;  but  if  the  heating  continues 
the  temperature  is  finally  reached  at  which  light  is  given 
off,  and  we  say  the  body  is  incandescent.  Heat  is  due 
to  the  motion  of  the  molecules.  As  the  temperature  in- 
creases the  molecules  strike  each  other  harder  and  finally 
cause  the  electrons  to  vibrate  rapidly  enough  to  produce 
the  sensation  of  light. 

The  velocity  of  light  is  so  great  that  for  many  years  it 
was  supposed  to  pass  instantly  from  its  source  to  any  dis- 
tance. In  1676  a  Danish  astronomer  by  the  name  of 
Roemer  determined  the  speed  to  be  186,000  miles  a 
second.  Other  experiments  have  verified  his  results. 

220 


LIGHT  221 

Light  travels  in  straight  lines  through  a  transparent 
medium  of  uniform  density. 

Sources  of  Light.  —  Much  of  the  light  we  enjoy  comes 
from  the  sun ;  but  since  the  sun  is  hidden  from  our  view 
for  one  half  the  time  of  each  year,  man  has  devised 
numerous  means  of  producing  artificial  light.  Whale- 
oil  lamps,  pine  knots,  candles,  kerosene  lamps,  gas  lamps, 
and  electricity  have  been  used  for  the  purpose  of  giving 
light.  The  light  of  flames  is  due  to  little  particles  of 
carbon  which  have  been  heated  to  incandescence  by  the 
combustion  of  gases  from  heated  oil  or  wax.  Most  light 
sources  are  quite  hot. 

Luminous  Bodies.  —  We  cannot  see  light  itself,  but 
we  can  see  the  bodies  which  emit  the  light.  Such  bodies, 
as  the  sun,  the  lighted  candle,  the  arc  light,  are  called 
luminous  bodies.  Every  point  in  a  luminous  body  sends 
out  rays  of  light  in  all  directions.  Most  of  the  objects 
we  see  are  non-luminous.  We  see  them  by  the  light  which 
they  receive  from  some  other  source  and  then  reflect  to 
our  eye.  If  a  non-luminous  object  reflects  no  light,  it 
is  invisible.  The  moon  is  a  non-luminous  body  and 
receives  its  light  from  the  sun. 

Transparent,  Translucent,  and  Opaque  Bodies.  - 
From  observation  we  have  learned  that  light  passes 
through  many  substances,  such  as  air,  glass,  water,  and 
mica.  Substances  through  which  objects  may  be  dis- 
tinctly seen  are  said  to  be  transparent.  Substances  which 
allow  some  of  the  light  to  pass,  but  through  which  ob- 
jects cannot  be  seen  distinctly  are  called  translucent. 
Parchment,  oiled  paper,  and  ground  glass  are  examples 
of  translucent  substances.  Substances  such  as  stone 
and  wood  through  which  light  does  not  pass  are  called 
opaque  substances. 


222 


GENERAL  SCIENCE 


Experiment  62.  —  Shadows.  —  Place  an  opaque  cylinder,  two  or 
three  inches  in  diameter,  in  a  dark  room.  Place  two  lighted  can- 
dles about  six  inches 
away  from  the  cylin- 
der, making  the  dis- 
tance between  the 
candles  equal  to  the 
diameter  of  the  cyl- 
inder (Figure  194). 
Is  there  any  space 


behind  the  cylinder 


FIG.  194. 

that  does  not  receive  light  from  either  candle?  Why  are  there  two 
light  shadows?  Could  we  have  used  one  large  source  of  light  in 
place  of -the  two  candles?  Explain. 


The  space  that  does  not  receive  light  from  either  candle 
is  called  the  umbra.  The  region  that  receives  light  from 
one  candle  only  is  called  the  penumbra. 

Figure  195  illustrates  a  total  eclipse  of  the  moon. 
When  the  moon  passes  into  the  umbra,  the  shadow  of 
the  earth,  a  total 
eclipse  of  the 
moon  occurs.  If 
the  moon  passes 
so  that  it  is  part 
in  the  umbra  and 
part  in  the  penumbra,  a  partial  eclipse  occurs. 

Light  as  Energy.  —  Light  does  work  so  quietly  that 
we  may  not  think  of  it  as  a  form  of  energy.  Light  has 
much  to  do  with  our  food  supply.  Plants  containing 
chlorophyll,  the  green  coloring  matter  of  our  vegetation, 
are  able  to  produce  starch,  sugar,  and  other  complex 
organic  substances,  when  stimulated  by  sunlight.  The 
change  which  takes  place  is  a  chemical  change,  and  the 
energy  required  is  supplied  by  the  sun  as  light.  These 


FIG.  195. 


LIGHT 


223 


substances  are  later  used  as  food  by  animals,  and  the 
energy  reappears  as  heat  energy  or  muscular  energy.  As 
we  continue  our  scientific  studies  we  will  observe  that 
energy  is  never  lost  or  destroyed.  It  is  often  changed 
in  form,  but  it  never  disappears. 

When  a  photographic  plate  is  exposed  to  light,  a  chem- 
ical change  takes  place.  New  substances  are  formed  on 
the  plate  in  such  a  way  that  when  properly  developed  a 
picture  may  be  produced  on  sensitized  paper.  It  is  this 
same  light  energy  which  affects  the  various  sensitized 
papers  used  in  photographic  and  blueprint  work. 

Experiment  63.  —  Intensity  of  Light.  —  Figure  196  furnishes  an 
illustration  of  the  way  the  intensity  of  light  is  affected  by  dis- 
tance. Let  L  be  a 
small  source  of  light 

and  A  a  screen  one         L  ,_--::rr^~" 

foot  square,  placed  ^v:-----U-.-"-._. 
at  a  distance  of  four 
feet  from  L.  Since 
light  travels  in 
straight  lines,  the 
area  of  the  shadow 
of  A  on  B  placed  eight  feet  from  L  will  be  four  square  feet. 

From  this  experiment  it  is  evident  that  the  light  which 
is  received  by  a  surface  having  an  area  of  one  square  foot 
is  scattered  over  an  area  of  four  square  feet  when  the  dis- 
tance from  the  light  source  is  doubled,  and  nine  square  feet 
when  the  distance  is  trebled.  A  pupil  who  sits  twice  as 
far  from  a  lamp  as  another  pupil,  receives  but  J  as  much 
light. 

How  Light  is  Measured.  --The  amount  of  light  given 
by  a  lamp  is  commonly  designated  as  a  certain  number  of 
candle  power.  A  candle  power  is  the  amount  of  light 
given  off  by  a  sperm  candle  known  as  "  sixes,"  meaning 


FIG.  196. 


224  GENERAL  SCIENCE 

six  candles  to  the  pound.     A  photometer  is  an  apparatus 
for  measuring  the  candle  power  of  light  sources. 

Bunsen  Photometer.  —  Place  a  drop  of  oil  on  a  sheet 
of  unglazed  white  paper.  When  we  hold  the  paper 
between  the  eye  and  the  window,  the  spot  appears  light. 
When  held  so  that  the  eye  is  between  the  paper  and  the 
window,  the  spot  appears  dark.  By  experimenting  we 
learn  that  when  the  paper  is  viewed  from  the  side  of  the 
greater  illumination  the  oiled  spot  appears  dark  but  when 
viewed  from  the  other  side  it  appears  light. 

Experiment  64.  —  Place  a  lighted  candle  A  at  a  distance  of  two 
decimeters  from  a  screen  S  having  in  its  center  a  square  of  oiled 

paper    (Figure   197). 
0n  the  other  side  of 
the  screen  place  the 
light  D  to  be  meas- 
ured, the  light  in  this 
case  being  that  of  an 
electric  bulb.     Move 
FIG.  197.  —  A  Simple  Arrangement  for  Measuring     J)  until  a  position  is 
the  Intensity  of  Light. 


oiled  paper  appears  the  same  from  either  side.  The  square  of  the 
distance  from  S  to  D  divided  by  the  square  of  the  distance  from 
A  to  S  will  give  the  candle  power  of  the  light  D.  Suppose  the 
distance  from  S  to  D  to  be  eight  decimeters.  Then  the  candle 
power  of  D  is  16,  since  64  divided  by  4  is  16.  The  room  must 
be  free  from  light  sources  excepting  those  used  in  the  experiment. 

Reflection  of  Light.  —  An  ordinary  piece  of  glass  both 
reflects  and  transmits  light.  Many  of  us  have  noticed 
the  reflection  of  the  open  fire  by  the  window-panes,  making 
it  appear  as  if  there  were  another  fire  outside.  On  the 
outside  of  the  window  the  fire  may  be  seen  by  transmitted 
light. 

Hold  a  mirror  so  that  the  sun's  rays  falling  upon  it 
will  appear  as  a  spot  of  light  on  the  wall  or  ceiling  of  the 


LIGHT 


225 


FIG.  198.  —  Angles  of  Incidence 
and  Reflection. 


room.  The  spot  of  light  has  been  reflected  by  the  bright 
surface  of  the  mirror.  The  rays  of  light  which  fall  upon 
the  mirror  are  called  incident  rays,  while  the  rays  which 
the  mirror  sends  off  to  the  wall  are  called  reflected  rays. 

Experiment  65.  —  From  stiff  cardboard  make  a  semicircle  having 
a  radius  of  twelve  inches  (Figure  198).  Support  the  cardboard  so 
that  the  line  marked  0°  is  perpendicular 
to  a  plane  mirror  on  which  it  rests. 
The  mirror  should  not  be  wider  than 
one  half  inch.  Thrust  a  bright-headed 
pin  through  the  semicircle  near  the  end 
of  one  of  the  lines.  Move  the  eye 
along  the  other  side  of  the  semicircle 
until  a  position  is  found  where  the  pin 
may  be  seen  in  the  mirror.  How  does 
the  angle  of  incidence  ABD  compare  with  the  angle  of  reflection 
CBDt  Make  readings  with  the  pin  in  a  number  of  different  posi- 
tions along  the  circumference.  Can  you  formulate  the  law  for  the 
reflection  of  light? 

The  Reflection  of  Light  as  Exhibited  in  the  Mirror.  - 

The  bouncing  of  balls  from  the  pavement  or  walls  and 

the  action  of  billiard  balls 
on  striking  the  cushion  of 
the  billiard  table  are  all 
'examples  of  reflection  sim- 
ilar to  the  reflection  of 
light  in  which  the  angle 
of  incidence  is  equal  to 
FIG.  199.  —  Diagram  showing  the  the  angle  of  reflection. 

An  object  viewed  in  a 
mirror  appears  to  be  behind 
the  mirror  a  distance  equal  to  the  distance  of  the  object 
in  front  of  it.  Figure  199  shows  the  position  of  such  an 
object.  MN  represents  a  vertical  mirror.  Rays  of  light 


Apparent  Position   of   an    Object   when 
Viewed  in  a  Mirror 


226 


GENERAL  SCIENCE 


from  the  tip  of  the  flame  strike  the  mirror  at  all  points, 
but  only  the  ray  which  strikes  the  mirror  at  F  is  reflected 
to  the  eye.  Why  ?  It  is  the  same  with  the  rays  of  light 
from  other  points  on  the  object  OA  ;  for  example,  only 
the  ray  from  A  which  strikes  the  mirror  at  B  will  reach 
the  eye.  The  eye  sees  the  image  of  0  at  0',  since  the 
line  O'F  is  a  continuation  of  the  direction  from  which 
the  ray  from  0  entered  the  eye. 

It  is  to  be  noted  that  as  you  face  the  mirror  the  left 
side  of  the  face  appears  as  the  right  side  in  the  mirror. 
It  is  difficult  to  tell  the  time  of  day  by  looking  at  the 
image  of  the  clock  in  the  mirror  for  this  reason.  Writing 
to  be  read  in  the  mirror  must  be  written  backwards. 

Diffused  or  Scattered  Light.  -  -  The  snow  reflects  the 
sunlight  in  countless  directions.  This  sort  of  reflection 
is  called  diffusion.  The  "  glare  "  of  the  sun  upon  the 
snow,  which  is  so  painful  to  weak  eyes,  is  due  to  the  fact 
that  no  matter  which  way  we  turn  we  encounter  strong 
reflected  light.  Most  objects  do  not  have  a  mirror-like 

surface  and  hence  diffuse  the 
light  which  strikes  them  in  all 
directions.  It  is  by  the  aid  of 
this  diffused  light  that  we  see 
these  objects.  Mirrors  are  some- 
times difficult  to  see  because  the 
reflection  of  the  light  upon  them 
is  so  nearly  perfect.  Rooms  with 
mirrored  walls  may  seem  to  be 
very  large  rooms. 

Refraction  of  Light.  —  A  number  of  familiar  phenomena 
are  due  to  the  refraction  of  light  or  the  bending  of  a  ray 
of  light  as  it  passes  from  one  transparent  medium  to 
another.  If  a  pencil  be  placed  in  a  tumbler  of  water, 


LIGHT  227 

it  will  seem  to  be  bent  where  it  enters  the  water.  Place 
a  coin  in  a  cup  with  opaque  sides  so  that  it  is  just  out  of 
view  (Figure  200) .  Keep  the  eye  fixed  on  the  same  place 
and  fill  the  cup  with  water.  The  coin  will  now  be  visible. 
Figure  201  represents  the  bending  of  a  beam  of  light  as 
it  enters  and  leaves  the  water.  The  reason  that  it  is  bent 
is  that  light  travels  slower  in  water  than  in  air.  The 
lower  side  of  the  beam  enters 
the  water  first  and  is  retarded 
so  that  the  upper  part  of  the 
beam  gets  ahead,-  thus  bend-  ^%/A  Air 

ing  it  toward  a  perpendicular 
as  shown  in  the  figure.  As 
the  beam  leaves  the  water, 
the  lower  part  reaches  the 
air  first  and  immediately  in- 
creases its  speed,  while  the  FIG.  201.— AS  light  passes  from 

/       ,  .       *"e  alr  mt°   the  water  at  an  angle 

Upper    part     Of    the    beam     IS    other  than  a  perpendicular  it  is  bent 

still  in  the  water.     Thus  it  is  or  refracted- 
bent  again  but  in  the  opposite  direction.     If  the  beam 
strikes  the  surface  of  the  water  at  right  angles,  it  will  not 
be  bent  in  either  direction. 

Light  is  bent  or  refracted  when  it  passes  obliquely  from 
one  transparent  medium  to  another  of  different  density. 
This  principle  is  of  great  importance,  since  it  is  the  one 
involved  in  the  eye  and  in  nearly  all  of  our  important  opti- 
cal instruments,  including  the  microscope,  the  telescope, 
camera,  and  stereopticon. 

Lenses.  —  There  are  a  great  many  practical  uses  made 
of  lenses.  They  are  used  in  cameras,  microscopes,  tele- 
scopes, spectacles,  field  and  opera  glasses,  stereopticons, 
and  other  similar  instruments. 

A  lens  is  usually  made  of  glass  and  has  two  curved  sur- 


228 


GENERAL  SCIENCE 


faces  or  one  curved  and  one  plane  surface.  The  curved 
surfaces  are  usually  spherical  and  may  have  any  of  the 
forms  shown  in  Figure  202.  There  are  two  general  classes 


FIG.  202.  —  Lenses  of  Different  Forms. 

of  lenses,  convex  lenses  which  are  thicker  at  the  middle 
than  at  the  edge  and  concave  lenses  which  are  thicker  at 
the  edge. 

Experiment  66.  —  Hold  a  double  convex  lens  in  the  sun's  rays. 
Scatter  some  crayon  dust  under  the  lens  and  notice  how  the  re- 
fracted rays  cortverge  to  one  point.  This  point  is  called  the  focus 
or  "  fireplace."  Hold  a  piece  of  tissue  paper  at  this  point.  What 
is  the  effect?  View  some  print  through  this  lens.  Does  the  lens 
magnify  or  not? 

Experiment  67.  —  Draw  the  blinds  on  all  the  windows  in  the 
room  except  one.  Hold  a  convex  lens  near  the  wall  opposite  the 
window,  and  then  move  it  until  a  clear  image  of  the  window  is 
thrown  on  the  wall.  The  distance  from  the  lens  to  the  wall  is 
called  the  focal  length  of  the  lens. 

When  rays  of  light  pass 
through  a  lens,  they  are  bent 
toward  the  thickest  part  of 
the  lens. 

Uses  of  the  Lens.  —  The 
*••>  simple  microscope  is  nothing 
FIG.  203.  —  A  Convex  Lens  Used  as  more  than  a  convex  lens  as 

a  Magnifying  Glass.  .        .~.  ^f\f\  * 

shown  in  Figure  203.      An 

object  viewed  through  such  a  lens  appears  in  its  natural 
position,  but  larger.  Spectacles  are  often  but  a  pair  of 
convex  lenses  of  small  magnifying  power. 


LIGHT 


229 


pi' 


The  compound  microscope  consists  of  a  convex  lens  0 
(Figure  204)  of  short  focal  length,  called  the  objective,  and 
a  larger  convex  lens  L  called  the  eye- 
piece. When  the  object  MN  is  viewed, 
an  image  is  formed  at  mn.  This  image 
is  further  magnified  by  the  eyepiece  so 
that  it  appears  as  M'N'. 

The  telescope  is  like  the  compound 
microscope  with  this  difference  —  the  ob- 
ject lens  is  made  large  for  collecting  a 
large  amount  of  light  (Figure  205). 

The  camera  is  a  light-proof  box  fitted 
with  convex  lenses.  Light  enters  the 
camera  through  the  lens,  which  produces 
on  a  ground  glass  at  the  rear  of  the  box 
an  inverted  image  of  the  objects  within 
the  range  of  the  lens  (Figure  206).  If  a 


Mirror 


sensitized  plate  or  film  is  substituted  for  FlG-  2,04A/rrA  Com" 

*  .  pound  Microscope. 

the  ground  glass,  a  picture  will  be  pro- 
duced by  the  chemical  action  of  the  light  on  the  plate 
or  film.      This  plate  is  now  treated   with  a  developing 
fluid,  which  brings  out  a  visible  and  permanent  image 


Totheobjtci 


FIG.  205.  — Telescope  Lenses.    ' 

of  the  objects  taken  in   the  picture.     The  plate  is  now 
called   a  negative,    because    the    light    and    shade    are 


230 


GENERAL  SCIENCE 


reversed  in  the  picture 
upon  it.  This  negative 
may  be  used  to  produce 
any  number  of  positive 
photographs  on  sensitized 
paper  (Figure  207). 

The  eye  is  essentially 
a  small  camera.  Light 
enters  the  eye  through  the  pupil,  which  corresponds  to 
the  shutter  of  a  camera.  It  then  passes  through  the 
crystalline  lens  (convex  lens)  into  the  dark  space  and 


FIG.  206.  —  Showing  the  Inversion  of  the 
Image  in  a  Pin-hole  Camera. 


FIG.  207.  —  Diagram  of  a  Camera. 

finally  forms  an  image  on  the  retina  at   the  back  of 
the  eye. 

Experiment  68.  —  Look  obliquely  through  a  block  of  glass 
(Figure  208)  and  set  four  pins,  two  on  each  side  of  the  block,  so 
that  they  form  a  straight  line.  Remove  the  block  and  draw  lines 
connecting  the  pins.  Are  they  in  a  straight  line? 


FIG.  208. 


LIGHT 


231 


The  Prism  and  Composition  of  White  Light.  —  If  sun- 
light be  allowed  to  fall  on  a  glass  prism  (Figure  209)  and 
the  refracted  rays  be  caught  on  a  white  screen,  a  beauti- 
ful band  of  colors  will  be  seen.  These  colors  in  their 
order  are  violet,  indigo,  blue,  green,  yellow,  orange,  and 


FIG.  209.  —  The  prism  separates  white  light  into  its  constituent  colors, 
which  are  arranged  as  shown. 

red.  The  violet  color  is  refracted  or  bent  from  its  original 
path  the  most ;  the  red  color  is  refracted  the  least.  From 
this  experiment  it  is  evident  that  the  white  light  from 
the  sun  is  composed  of  these  several  colors.  The  entire 
band  of  colors  is  called  the  solar  spectrum,  and  the  process 


FIG.  210.  —  A  piece  of  paper  placed  between  the  prisms  will  show 
the  separated  colors. 

of  separating  colors  by  refraction  is  called  dispersion. 
If  the  solar  spectrum  made  by  a  prism  is  passed  through 
a  similar  prism  in  a  reversed  position  (Figure  210),  the 
several  colors  will  be  reunited  to  form  a  single  band  of 
white  light. 


232 


GENERAL  SCIENCE 


Length  of  Light  Waves 

Violet.     .     .',.     .000397mm.      Yellow.     .     .     .     .000589mm. 
Indigo 000430  mm.      Orange  ....     .000656  mm. 


Blue     ....     .000480  mm. 
Green  .  .000527  mm. 


Red  .  .000689  mm. 


In  the  solar  spectrum  we  notice  that  the  bending  in- 
creases as  the  wave  length  decreases,  the  bending  being 
greater  for  the.  violet  light.  The  reason  for  the  bending 
of  a  ray  as  it  strikes  a  transparent  medium  obliquely  is 
that  its  speed  is  changed,  and  the  greater  the  change  in 
speed  the  greater  the  bending.  Therefore,  since  the  vio- 
let light  was  bent  more  than  the  red  light,  the  speed  of 
violet  light  in  glass  must  be  less  than  that  of  red. 

Red  light  waves  are  the  longest  and  have  the  least 
frequency  of  light  waves  producing  visible  rays.  When 
a  piece  of  iron  is  heated  to  incandescence,  it  first  gives  off 
red  light.  As  the  heating  continues  the  activity  of  the 
molecules  and  .electrons  increases,  producing  shorter 

light   waves   and    conse- 
quently a  change  in  color 
to  almost  a  pure  white. 
The  rainbow  is  a  solar 


FIG.  21 1 .  —  An  Artificial  Rainbow. 


spectrum  on  a  large  scale. 
Rainbows  are  caused  by 
the  dispersion  of  sunlight 
by  drops  of  rain.  They 
may  be  seen  only  in  the 
morning  and  late  after- 
noon, since  the  sun  must  not  be  higher  than  42°  from  the 
horizon.  In  order  to  see  a  rainbow  it  is  necessary  to  look 
at  falling  raindrops  upon  which  the  sun  is  shining  from 
a  position  behind  you.  Miniature  rainbows  may  be  seen 
in  the  spray  from  fountains  or  lawn  sprinklers  (Figure  211). 


LIGHT  233 

Absorption  of  Light  and  Color  Phenomena.  —  Color 
depends  upon  the  wave  length  of  light.  Only  wave  lengths 
within  a  certain  limit  affect  the  nerves  of  sight,  namely 
those  between  .0000689  cm.  and  .0000397  cm.  in  length. 
There  are  many  ether  waves  both  longer  and  shorter  than 
these,  but  they  are  not  visible.  White  light  contains 
all  the  colors  of  the  spectrum  from  red  to  violet  inclusive. 
Most  artificial  light  is  deficient  in  some  of  the  colors  of 
the  spectrum  and  is  therefore  not  white  light.  For  ex- 
ample, the  mercury  vapor  electric  lamp  gives  a  light 
which  is  deficient  in  red  waves.  When  objects  are 
viewed  in  such  a  light,  they  have  a  ghostly  appearance. 
Why? 

If  a  piece  of  red  glass  is  held  in  the  path  of  the  spec- 
trum, all  the  colors  except  the  red  will  disappear,  showing 
that  all  the  wave  lengths,  except  the  wave  length  which 
produced  red,  have  been  absorbed  by  the  glass.  Try 
glass  of  other  colors  in  the  same  way.  It  will  be  found 
that  glass  of  certain  colors  has  greater  power  of  absorbing 
light  than  glass  of  other  colors.  Red  is  one  of  the  best 
absorbers  of  other  colors. 

Most  substances  absorb  light  to  some  degree.  The 
absorbed  light  reappears  as  heat  energy  or  chemical 
energy.  The  light  that  falls  on  an  object  and  is  not  ab- 
sorbed is  reflected.  The  color  which  a  body  has  in  or- 
dinary daylight  is  determined  by  wave  lengths  which  are 
not  absorbed  by  the  body.  If  a  body  appears  white  in 
daylight,  it  is  because  it  reflects  or  disperses  all  wave 
lengths  and  does  not  absorb  one  kind  of  wave  length  more 
than  the  other.  If  a  body  appears  red  in  daylight,  it  is 
because  it  absorbs  other  rays  more  readily  than  it  does 
red  rays,  so  that  the  light  which  is  reflected  contains  a 
large  proportion  of  red  waves.  A  body  appears  blue  or 


234  GENERAL  SCIENCE 

green  or  yellow  in  daylight  when  it  absorbs  less  of  one  of 
these  colors  than  it  does  of  the  other  colors  contained  in 
white  light.  So  we  see  that  color  is  really  not  a  property 
of  bodies,  but  is  the  sensation  that  a  body  produces  when 
we  view  it  in  daylight.  If  viewed  in  light  other  than  day- 
light, objects  will  often  produce  different  color  sensations. 
For  example,  a  green  ribbon  will  not  appear  green  unless 
viewed  in  light  containing  green  rays. 

Sometimes  a  certain  combination  of  colors  will  produce 
white  light  even  when  part  of  the  spectrum  is  lacking. 
Two  colors  that  will  produce  white  light  when  mixed  are 
called  complementary  colors.  Red  and  bluish  green, 
orange  and  light  blue,  light  green  and  violet  are  such 
combinations.  . 

QUESTIONS 

1.  Name  six  luminous  bodies. 

2.  Name  six  non-luminous  bodies. 

3.  Is    the    earth    luminous    or    non-luminous?     The    moon? 
What  reasons  have  you  for  thinking  so? 

4.  How  may  we  change  a  piece  of  iron  from  a  non-luminous  to 
a  luminous  body? 

5.  If  the  sun  is  92,000,000  miles  from  4;he  earth,  how  long  does 
it  take  light  to  travel  from  the  sun  to  the  earth? 

6.  The  report  of  a  gun  is  heard  two  seconds  after  the  flash  is 
seen.     How  far  away  is  the  gun? 

7.  A  flash  of  lightning  is  seen  five  seconds  before  the  thunder 
is  heard.     How  far  away  is  the  cloud? 

8.  Name  four  transparent  substances.     Four  translucent  sub- 
stances.    Four  opaque  bodies. 

9.  Gold    is    ordinarily   opaque.     May   it    be    hammered    thin 
enough  to  be  translucent? 

10.  One  book  is  held  three  feet  and  another  book  is  held  nine 
feet  away  from  the  lamp.     How  many  times  as  much  light  does  the 
first  book  receive  as  the  second  book? 

11.  What  are  the  positions  of  the  sun,  moon,  and  earth  when  we 
have  an  eclipse  of  the  sun  ?     An  eclipse  of  the  moon  ? 


LIGHT  235 

12.  Lay  a  triangular  prism  over  and  parallel  to  a  pencil  mark. 
How  many  marks  appear?     Explain. 

13.  Why  do  we  not  see  rainbows  near  noon? 

14.  In  problems  6  and  7  of  this  list  why  may  we  neglect  the 
speed  of  light? 

The  Sight.  -  -  The  eyes  are  the  very  complex  external 
organs  in  which  the  fibers  of  the  optic  nerve  terminate,  and 
by  means  of  which  sight  impulses  are  produced.  The 
optic  nerve  is  stimulated  by  light ;  but  the  structure  of 
the  eye  is  such  that  there  is  not  a  flood  of  light  falling 
upon  the  termini  of  the  nerve  fibers  but  a  perfect  image 
of  the  lighted  objects  in  the  field  of  vision. 

Protection  of  the  Eyes.  -  -  The  eyeballs  are  two  nearly 
spherical  bodies.  They  are  admirably  protected  by  being 
set  into  deep  sockets.  These  sockets  are  lined  with 
fatty  tissue  in  such  a  way  as  to  protect  the  eyes  from 
shocks.  The  eyeballs  are  further  protected  by  movable 
folds  of  the  skin  called  eyelids,  and  the  eyebrows.  The 
eyelids  are  fringed  by  a  row  of  stiff  hairs  which  keep  out 
dust  particles  and  help  to  shade  the  eye  from  irritating 
lights.  They  are  lined  with  a  mucous  membrane  called 
the  conjunctiva  and  fit  the  front  of  the  eyeball  perfectly. 
Friction  between  the  eyelids  and  the  eyeball  is  prevented 
by  mucous  secreted  by  the  conjunctiva  and  tears  or 
lachrymal  fluid  secreted  by  the  lachrymal  gland.  Ex- 
cess lachrymal  fluid  is  drained  into  the  nose  through  a 
small  duct  called  the  lachrymal  duct.  The  flow  of  the 
lachrymal  fluid  is  increased  by  irritations  of  the  covering 
of  the  eye  or  by  strong  emotion.  In  such  cases  the  lach- 
rymal duct  is  unable  to  drain  the  fluid  off  fast  enough, 
and  tears  overflow  on  to  the  face. 

The  movements  of  each  eye  are  controlled  by  six  muscles 
so  arranged  that  the  eyeball  may  be  turned  in  any  direction. 


236 


GENERAL  SCIENCE 


Cornea 
trfi- 


Structure  of  the  Eyeball.  -  -  The  eyeball  has  a  diameter 
of  about  one  inch.  Except  at  the  front  and  at  the  place 
where  the  optic  nerve  enters,  the  eye  is  covered  with 
an  opaque,  white  coat  called  the  sclerotic  coat  (Figure  212). 
This  coat  forms  the  white  of  the  eye  "and  the  transparent 

modification  of  it  at 
the  front  of  the  eye 
is  called  the  cornea. 
Inside  the  sclerotic 
coat  is  a  second  layer 
called  the  choroid. 
This  coat  contains  a 
network  of  blood  ves- 
sels and  is  colored  black 
by  pigment  cells  so  that 
it  appears  like  the  in- 
side of  a  dark  grape 
skin.  The  dark  sur- 
face of  this  coat  absorbs  the  rays  of  light  which  would 
otherwise  be  reflected  and  interfere  with  perfect  vision. 
In  albinos  this  coat  has  no  dark  pigment  cells,  and  the 
vision  is  therefore  imperfect  in  strong  light. 

At  the  front  of  the  eye  the  choroid  coat  is  continued 
as  a  muscular  curtain  known  as  the  iris.  At  the  center 
of  the  iris  is  a  round  opening  (the  pupil)  through  which 
the  light  enters  the  eye.  The  size  of  the  pupil  is  regu- 
lated by  the  involuntary  muscles  of  the  iris,  of  which 
there  are  two  sets,  one  circular,  and  the  other  radiating. 
The  contraction  of  the  circular  muscle  fibers  decreases  the 
size  of  the  pupil,  and  the  contraction  of  the  radial  fibers 
increases  the  size  of  the  pupil.  The  iris  is  colored  by 
pigment.  When  we  speak  of  a  person's  eyes  as  blue  or 
gray  we  simply  mean  that  these  colors  are  the  predorni- 


FIG.    212.  —  Showing    a   Section    of   the 
Eyeball. 


LIGHT  237 

nating  colors  in  the  iris.  The  outer  edge  of  the  iris  is 
fastened  to  the  sclerotic  coat  by  the  ciliary  ligament  and 
to  the  choroid  coat  by  folds  known  as  ciliary  processes. 

The  third  layer  of  the  eye  or  retina  is  a  delicate  trans- 
parent membrane  of  connective  tissue  containing  an 
expansion  of  the  optic  nerve.  It  lines  the  interior  of  the 
eyeball  with  the  exception  of  the  front,  where  it  stops  with 
the  ciliary  processes  and  at  the  entrance  of  the  optic 
nerve.  The  retina  is  the  only  part  of  the  eye  that  is 
sensitive  to  light,  and  it  is  the  part  of  the  eye  in  which 
visual  impulses  originate. 

In  addition  to  the  transparent  parts  of  the  eye  al- 
ready mentioned  there  are  three  other  important  media. 
The  main  part  of  the  interior  of  the  eyeball  is  filled  with 
a  colorless,  transparent,  jelly-like  substance  called  the 
vitreous  humor.  It  aids  in  preserving  the  form  of  the 
eyeball.  In  front  of  the  vitreous  humor  and  just  behind 
the  iris  is  the  crystalline  lens.  It  is  a  biconvex,  transpar- 
ent body  which  focuses  the  rays  of  light  as  they  enter  the 
eye,  so  that  a  clear  image  of  the  reflecting  object  is  pro- 
duced. Between  the  crystalline  lens  and  the  cornea  is 
a  small  space  which  is  filled  with  a  clear,  watery  liquid 
called  the  aqueous  humor. 

The  place  where  the  optic  nerve  enters  the  eye  is  called 
the  "  blind  spot,"  since  the  eye  at  that  point  is  not  sen- 
sitive to  light. 

How  the  Eye  Does  its  Work.  —  The  human  eye  re- 
sembles a  camera  in  many  essential  respects.  It  con- 
tains a  focusing  lens,  the  crystalline  lens,  the  iris,  which 
acts  as  a  shutter,  and  the  retina,  which  takes  the  place  of 
the  camera  film  or  sensitive  plate  (Figure  213).  The  eye, 
however,  is  vastly  superior  to  the  camera.  The  focusing 
organs  of  the  eye  possess  the  power  of  accommodating 


238 


GENERAL  SCIENCE 


FIG.  213.  — Two  Cameras. 
A  diagram  showing   the  similarity  in 
the  structure   of   a  photographic   camera 
and  the  eye. 


their  shapes  so  that  objects  at  different  distances  may 
be  properly  focused.  The  crystalline  lens  is  elastic  and 
would  become  more  convex  if  it  were  not  held  under 

tension  by  the  suspen- 
sory ligament  which  is 
attached  to  the  choroid 
coat.  When  the  distance 
of  the  object  requires  a 
change  of  focus,  the  cil- 
iary muscles  draw  the 
choroid  coat  forward, 
thus  reducing  the  tension 
on  the  crystalline  lens. 
The  lens  immediately  be- 
comes more  convex  and 
shortens  its  focus.  When  the  ciliary  muscles  are  relaxed 
the  crystalline  lens  is  pulled  back  to  its  original  position. 
The  shutter  (iris)  in  the  eye  works  automatically,  al- 
lowing the  proper  amount  of  light  to  enter  the  eye  at  all 
times.  The  retina  is  also  superior  to  the  camera.  While 
the  photographic  plate  can  be 
used  but  once,  the  retina  is  able 
to  receive  any  number  of  impres- 
sions and  send  them  to  the  brain 
for  record.  In  other  words,  the 
camera  of  the  eye  is  always 
"  loaded." 

The  image  formed  on  the  ret- 
ina is  always  inverted  (Figure 
214),  but  this  does  not  prevent  our  seeing  the  object  in 
its  correct  position ;  since  it  is  the  brain  which  translates 
the  visual  impulse  of  the  retina  into  the  sensation  of 
actual  sight, 


FIG.  214.  —  Showing  the 
Formation  of  an  Image  upon 
the  Retina. 


LIGHT  239 

Most  objects  are  non-luminous,  every  point  sending  out 
rays  of  reflected  light.  The  rays  that  enter  the  eye  are 
focused  in  proper  scale  by  the  cornea  and  crystalline  lens. 
If  for  any  reason  these  rays  are  not  properly  focused, 
defective  vision  results.  For  example,  "  near  sight  " 
results  when  the  focus  is  too  short  and  the  rays  meet  and 
cross  in  front  of  the  retina.  ."  Near  sight  "  may  be  cor- 
rected by  the  use  of  a  concave  lens  in  front  of  the  eye. 
"  Far  sight  "  is  due  to  the  focus  falling  at  a  point  behind 
the  retina.  Convex  lenses  are  used  to  remedy  this  de- 
fect. Astigmatism  is  due  to  imperfections  in  the  cur- 
vature of  the  cornea. »  The  light  which  falls  on  some 
particular  spot  of  the  cornea  is  not  properly  refracted. 
A  good  oculist  usually  can  correct  these  defects  in  vision 
and  should  be  consulted  whenever  they  appear. 

QUESTIONS 

1.  How  are  the  eyes  protected? 

2.  Of  what  value  are  tears? 

3.  Where  are  the  lachrymal  glands  situated? 

4.  Through  what  eye  media  does  the  light  pass  on  its  way  to 
the  retina? 

5.  Why  is  the  inside  of  a  camera  black? 

6.  What  coat  of  the  eye  may  be  compared  to  the  black  interior 
of  the  camera? 

7.  To  what  is  the  color  of  the  eye  due? 

8.  What  is  the  use  of  the  vitreous  humor  of  the  eye? 

9.  What  is  meant  by  the  power  of  "  accommodation  "  as  ap- 
plied to  the  eye? 

10.  What  causes  the  iris  to  dilate  and  contract? 

11.  Why  can  we  not  see  the  spokes  of  a  rapidly  moving  wheel? 

12.  The  film  of  a  moving-picture  machine  is  really  standing  still 
when  the  picture  is  thrown  on  the  screen.     Why  does  it  seem  to 
be  in  motion? 

13.  Name  some  cautions  to  be  observed  in  the  care  of  the  eyes. 

14.  What  is  "  color  blindness"? 


240 


GENERAL  SCIENCE 


Light  in  the  House.  —  In  recent  years  a  great  deal  of 
attention  has  been  given  to  the  problem  of  proper  light- 
ing for  different  kinds  of  buildings.  The  manufacture 
of  cheap  glass  has  made  it  possible  to  have  sunlight  in 
abundance  in  all  rooms  with  an  outside  exposure.  It  is 
quite  important  from  the  standpoint  of  health  that  we 
have  plenty  of  sunlight  in  our  homes  and  working  places, 

since  darkness  fosters  the 
collection  of  dirt  and  filth 
and  the  growth  of  disease 
germs. 

A  few  generations  ago 
sunlight  in  the  home  was 
a  luxury  because  of  the 
scarcity  of  transparent 
materials  which  could  be 
used  in  windows. 

How  Glass  is  Made.— 
It  is  quite  certain  that 
the  Egyptians  and  Phoe- 
nicians knew  how  to 
make  glass  long  before 
the  Christian  Era,  but 
it  was  not  until  the  six- 
teenth century  that  win- 
dow glass  was  first  used ;  and  then  for  many  years  it 
was  used  only  by  the  most  wealthy. 

Glass  commonly  is  made  by  melting  together  the  sili- 
cates of  calcium  and  sodium,  or  we  may  say  by  melting 
together  a  mixture  of  sand,  limestone,  and  soda.  The 
mixture  is  melted  in  pots  of  fire  clay.  This  is  the  soft 
glass  which  is  used  in  making  windows  and  ordinary 
glass  dishes.  If  potassium  silicate  is  used  instead  of 


Copyright  by  Underwood  &  Underwood,  N.  Y. 
FIG.  215.  — Glass  Bottle  Making. 
Blowing  a  bottle  and  shaping  bottom 
of  carboy  base. 


LIGHT  241 

sodium  silicate,  a  harder  glass  results.  This  glass  is 
known  by  such  names  as  hard  glass,  Bohemian  glass,  and 
crown  glass  (Figures  215,  216). 

Artificial   Lighting.  —  A   history   of    artificial   lighting 
includes  stories  of  the  use  of  many  different  materials. 


Copyright  by  Underwood  &  Underwood,  N.  Y. 
FIG.  216.  —  Glass  Making. 
Casting  and  rolling  sheets  of  plate  glass,  12^  X  21  feet,  Tarantum,  Pa. 

Prior  to  1860  the  common  means  of  lighting  were  the 
burning  of  wood  in  the  fireplace  —  pine  knots  gave  the 
most  light  because  of  the  turpentine  they  contained  — 


242 


GENERAL  SCIENCE 


and  the  burning  of  heavy  oils  either  in  open  dishes  or  in 

the  form  of  candles.     Lard,  olive  oil,  and  whale  oil  were 

the   oils  commonly   used  (Figure 
217). 

Candles  were  originally  made 
by  dipping  a  wick  into  melted  fat 
and  allowing  it  to  cool,  repeating 
the  operation  until  the  candle  was 
of  the  desired  thickness.  Candles 
are  now  made  of  fats  and  different 
waxes.  The  wick  is  set  in  a  mold 

FIG.  217.— A  whaie-oii  Lamp.    and  the  melted  material  is  poured 

around  it.    .When  it  has  solidified,  it  is  removed  from 

the  mold  and  is  ready  for  use. 

The  Kerosene  Lamp.  -  -  The   discovery  of  petroleum 

gave   a   distinct   impetus   to   lighting  problems.     Many 

forms  of   the   kerosene   lamp   were 

placed  on  the  market.     The  success 

of  the  kerosene  lamp  requires  that 

the  kerosene  be  burned  in  a  good 

supply  of  air ;    otherwise  the  lamp 

will  smoke  (Figure  218). 

Gases  for  Lighting.  -  -  There  are 

a  number  of  gases  which  may  be 

used    for    lighting    -purposes    with 

proper  burners.     When  soft  coal  is 

heated  in  a  retort,  illuminating  gas 

is  formed.      However,  most  of  the 

gas  which  is  sold  as  illuminating  gas 

is  formed  by  passing  steam  through  a 

hot  bed  of  coke  or  hard  coal.     This  water  gas  has  a  high 

fuel  value  but  burns  with  an  almost  colorless  flame,  giv- 
ing little  or  no  light.     In  order  that  it  may  be  used  for 


A 


FIG. 


218.  —  A  Kerosene 
Lamp. 


LIGHT 


243 


illuminating  purposes  petroleum  is  sprayed  into  the  hot 
carburetor  of  the  gas-producing  apparatus.  The  heat 
breaks  the  oil  into  gases  which  give  illuminating  power 
to  the  water  gas. 

As  illuminating  gas  reaches  the  consumer,  it  burns 
with  a  bright  yellow  flame.  To  prevent  smoking, 
it  is  burned  from  a  narrow  slit  burner  in  order 
that  more  of  its  surface  will  come  in  contact  with 
the  air. 

This  gas  is  stored  by  the  gas  companies  in  large  tanks 
inverted  in  water.  The  tanks  are  quite  heavy  and 
cause  the  gas  pressure  in  the  distributing  lines.  As  gas 
is  used  the  tanks  sink  into  the  water,  and  as  more  gas  is 
pumped  into  them  they  rise  again. 

Natural  Gas.  —  In  some  regions  large  pools  of  natural 
gas  are  found.  So  far  as  is  known  the  United  States 
has  a  greater  supply  of  this  gas  than  any 
other  nation.  It  is  a  most  perfect  fuel  and 
may  be  used  for  lighting  purposes  if  an 
incandescent  mantle  is  used.  To  use  a 
mantle  we  simply  burn  the  gas  in  a  Bun- 
sen  burner  and  suspend  the  mantle  over 
the  colorless  flame.  The  light  comes  from 
the  materials  of  the  mantle  which  are 
heated  to  incandescence  (Figure  219). 

The  best  mantles  are  made  by  soaking 
the  little  knitted  sack   in   a    solution    of 
cerium  and  thorium  salts.    When  the  sack 
is  dry,  the  solid  salts  fill  the  spaces  between 
the  threads.     The  mantlets  now  set  on  fire.     The  thread 
burns,  leaving  a  thin  shell  of  the  oxides  of  the  metals. 
Other  gases  besides  natural  gas  may  be  used  with  in- 
candescent mantles. 


FIG.  219.  —  A  Gas 
Mantle. 


Y 


244  GENERAL  SCIENCE 

Acetylene.  --  The  gas  is  made  by  the  action  of  calcium 
carbide  and  water.  When  thoroughly  mixed  with  air 

(Figure  220),  it  burns 
with  a  smokeless  flame 
of  brilliant  whiteness. 

Electric  Lighting. - 
The  most  common  method 
of   lighting   in    cities   at 
-*-  the  present  time    is   by 

FIG.  220.  — An  Acetylene  Burner  and       electricity,    Using    the   hl- 

candescent  electric  lamp, 
the  principle  of  which  has  already  been  given  (cf.  p.  202). 

Lighting  Fixtures.  —  The  last  few  years  have  pro- 
duced many  changes  in  the  prevailing  types  of  lighting 
fixtures.  Some  of  the  shades  and  globes  are  very  wasteful 
of  light  without  possessing  much  compensating  beauty. 
Indirect  lighting  is  very  wasteful  of  light,  and  it  is  also 
tiring  on  the  eyes.  The  best  light  for  the  eyes  will  be  a 
well-diffused  light  with  areas  of  light  and  shadow  as  is 
found  in  the  sunlight.  Indirect  lighting  is  well  diffused 
but  throws  no  well-defined  shadows,  which  are  so  es- 
sential to  normal  sight.  Probably  the  light  bowl  which 
best  meets  the  requirements  of  beauty  and  hygiene  is 
the  translucent  bowl,  which  while  it  reflects  some  of  the 
light  to  the  ceiling  also  diffuses  much  of  it  directly  into 
the  room.  This  is  called  semi-indirect  lighting. 

For  factories  direct  lighting  will  be  the  best  and  most 
economical. 

QUESTIONS 

1.  What   materials  were   used    in  windows  before  glass  came 
into  use  ? 

2.  What  is  "  Jena  "  glass? 

3.  How  was  the  whale-oil  lamp  made? 


LIGHT  245 

4.  When  was  petroleum  discovered?     By  whom?     Where? 

5.  Why  do  kerosene  lamps  sometimes  smoke? 

6.  What  kind  of  incandescent  bulbs  are  most  economical? 

7.  Why  does  a  carbon  filament  light  bulb  become  hotter  in 
use  than  a  Tungsten  light  bulb? 

8.  How  did  the  manufacture  of   cheap   glass   advance   civili- 
zation? 

9.  What  is  a  fuse  plug? 

10.    Explain  how  to  read  your  gas  meter.     Your  electric  meter. 


CHAPTER  XIV 
ELEMENTS,   COMPOUNDS,   AND   MIXTURES 

Interrelation  of  the  Sciences.  —  The  different  branches 
of  science,  such  as  physics,  chemistry,  biology,  physical 
geography,  and  botany,  are  not  separated  by  any  very 
definite  boundaries,  as  we  shall  see.  In  the  study  of  phys- 
ical geography  we  must  know  something  of  the  other 
sciences  in  order  to  understand  the  changes  that  have 
occurred  and  are  occurring  in  the  life  of  the  earth. 
Weathering  depends  upon  both  physical  and  chemical 
changes.  Winds  are  caused  by  heat,  a  physical  agent. 
A  study  of  plants  and  animals  involves  the  study  of  nu- 
merous physical  and  chemical  changes.  So  we  could  go 
on  citing  example  after  example  of  the  ways  in  which  the 
sciences  interlock  and  are  dependent  upon  one  another. 

How  matter  is  changed.  —  We  may  change  most 
substances  in  many  ways.  If  we  apply  heat  to  a 
piece  of  iron,  it  becomes  hot ;  as  more  heat  is  applied  it 
becomes  red  hot  and  gives  off  light.  If  the  heating  con- 
tinues, the  iron  finally  melts  and  may  be  poured  into  a 
different  form.  As  the  liquid  iron  cools  it  passes  back 
through  these  various  changes  and  finally  becomes  a  cold, 
black  piece  of  iron  again.  A  piece  of  iron,  when  rubbed 
with  a  magnet,  itself  becomes  a  magnet  and  exhibits  the 
property  of  attracting  pieces  of  iron  and  steel.  After  a 
time  the  magnetism  is  lost.  Through  these  various 
changes  the  iron  has  never  ceased  to  be  iron. 

246 


ELEMENTS,  COMPOUNDS,  AND  MIXTURES       247 

A  piece  of  ice  when  heated  changes  to  water.  If  the 
heating  is  continued,  the  water  is  changed  to  an  invisible 
gas  and  passes  into  the  air.  By  cooling  the  air  the  water 
may  be  recovered.  It  has  never  ceased  to  be  water  in 
some  form.  Are  these  changes  physical  or  chemical 
changes  ? 

When  a  piece  of  iron  wire  is  burned  in  oxygen,  a  new 
substance,  iron  oxide,  is  formed.  The  red  rust  that 
forms  on  iron  when  it  is  left  out  of  doors  or  in  a  damp 
place  is  this  same  new  substance.  When  iron  and  hydro- 
chloric acid  are  put  into  a  flask  together,  they  react  to 
form  a  new  substance,  iron  chloride,  and  hydrogen  is 
liberated.  These  new  substances  have  properties  which 
are  quite  different  from  those  of  iron. 

What  kind  of  changes  are  these  ? 

Oxidation.  -  -  The  union  of  any  other  element  with 
oxygen  is  called  oxidation,  and  the  new  substance  is  called 
an  oxide. 

Oxygen  is  the  most  abundant  of  the  elements,  and 
oxidation  is  the  most  common  chemical  change. 

The  rusting  of  iron  and  the  rotting  of  wood  are  ex- 
amples of  slow  oxidation.  When  we  say  that  a  substance 
oxidizes,  we  mean  that  one  or  more  of  its  elements  com- 
bines with  the  oxygen  of  the  air.  If  the  oxidation  takes 
place  rapidly,  it  is  called  combustion  or  burning.  In 
such  cases  measurable  quantities  of  light  and  heat  are 
given  off.  Heat  is  developed  in  the  decay  of  wood,  but 
the  process  is  so  slow  that  the  change  in  temperature  is 
too  small  to  be  noticeable. 

Elements,  Compounds,  and  Mixtures.  —  Many  sub- 
stances are  the  result  of  a  combination  of  two  or  more 
other  substances.  For  example,  hydrogen  and  oxygen 
combine  to  form  water;  iron  and  oxygen  combine  to 


248  GENERAL  SCIENCE 

form  iron  oxide;  zinc  and  sulphur  when  heated  combine 
to  form  a  white  powder,  zinc  sulphide.  Substances  which 
have  been  formed  by  the  union  of  two  or  more  substances 
are  called  compounds.  By  proper  means  these  com- 
pounds may  be  separated  again  into  the  substances  which 
were  used  in  their  production.  The  question  of  course 
arises  as  to  whether  these  substances — oxygen,  hydrogen, 
iron,  zinc,  sulphur  —  may  be  further  divided  into  other 
substances.  All  we  can  say  is  that  they  have  never  been 
divided  in  any  of  the  numerous  attempts  that  have  been 
made,  and  we  therefore  assume  that  they  cannot  be 
divided.  Substances  which  we  have  never  been  able  to 
decompose  into  other  substances  are  called  elements. 
If  powdered  zinc  and  sulphur  are  placed  in  a  dish  and 
stirred,  they  do  not  unite  but  remain  as  small  particles 
of  zinc  and  sulphur.  This  is  called  a  mixture.  When  a 
flame  is  brought  near  this  mixture,  there  is  a  flash  of 
light  and  a  cloud  of  white  smoke.  The  white  powder 
that  is  left  in  the  dish  is  no  longer  a  mixture  of  zinc  and 
sulphur  but  a  new  substance,  zinc  sulphide,  having  new 
properties.  Sulphur  will  dissolve  in  carbon  disulphide. 
Zinc  sulphide  will  not.  Sulphur  is  yellow  and  zinc  is 
gray.  The  new  substance  is  white. 

There  are  numerous  mixtures  about  us.  Air  is  a  mix- 
ture of  the  gases  nitrogen,  oxygen,  carbon  dioxide,  and 
water  vapor.  Most  rocks  are  mixtures  of  different  sub- 
stances. A  mixture  of  oxygen  and  hydrogen  does  not 
produce  water  until  the  temperature  is  raised  to  about 
620°  Centigrade. 

The  Common  Elements.  -  -  There  are  about  eighty  dif- 
ferent elementary  substances  or  elements,  but  many  of 
these  are  found  in  very  small  quantities.  In  our  daily 
life  we  are  not  commonly  concerned  with  more  than 


ELEMENTS,   COMPOUNDS,  AND   MIXTURES        249 


twenty  of  the  elements.  Twelve  of  these  are  always 
found  in  living  matter,  and  six  more  are  sometimes  found 
in  living  matter.  The  twelve  which  are  always  found  are  : 
phosphorus,  sulphur,  carbon,  oxygen,  hydrogen,  nitrogen, 
chlorine,  potassium,  sodium,  calcium,  magnesium,  and 
iron. 

Only  about  one  fourth  of  the  elements  are  found  in 
uncombined  state.  The  others  are  found  only  as  com- 
pounds. 


The  following  table  is  an  estimate  of  the  plentifulness 
of  the  elements.  Twelve  of  them  make  up  99  per  cent 
of  the  earth  (Figure  221). 


Per  Cent 

Oxygen 
Silicon    . 
Aluminum . 
Iron 
Calcium 
Sodium 


50.00 
26.00 
7.25 
4.10 
3.15 
2.30 


Per  Cent 

Potassium  . 
Magnesium  . 
Hydrogen 
Titanium .  . 
Chlorine  .  . 
Carbon 


2.30 

2.10 

1.00 

.40 

.20 

.20 


All  the  other  elements,  including  gold,  silver,  sulphur, 
and  mercury,,  make  up  the  remaining  one  per  cent  of  the 
earth. 


250 


GENERAL  SCIENCE 


PARTIAL  LIST   OF  ELEMENTS 


NAME 


SYMBOL 


STATE 


Aluminum      .     .     .     .     i  -   . ' •.  .     .  Al  Solid 

Antimony .     . Sb 

Arsenic      •..    ..     .....     .     .  As 

Barium      .     .     . Ba 

Bismuth    ...     .....     .  Bi 

Cadmium  .     .     .     .     .     .     •.     .     .  Cd 

Calcium     ...     .     ...     .  ' .     .  Ca 

Chromium .     .  Cr 

Cobalt  .     .     .     .   . .     .....  Co 

Copper .     .    \     .     .     .     .     ...  Cu 

METALS  ^old      •'-     -    -    V    "   -  -••'••   •  £u 

Iron Fe 

Load     .     .'     .     .     .     .     .     .     ..     .  Pb 

Magnesium    .     .     .     .     ...     .  Mg 

Manganese     .     ...  .     .     .     .     , '    .  Mn 

Mercury    .     .     .     ......     .  Hg         Liquid 

Nickel  .     .     .     .     .     ;     ..  - . .  •  .     .  Ni  Solid 

Platinum   .     .     .     .     .     .     v  .     •  Pt 

Silver    .     .     .....     .     .     ...  Ag 

Sodium '.     .'    .     .  Na 

Tin  .....     .     ,     .     ...  Sn 

Zinc.     .     .     .  *  .     .     .  '  .     .     .     .  Zn 

Boron .     .  B 

Carbon       .........  C 

Iodine I 

Phosphorus P 

Silicon  .    -.    -.     .     ....   "'.     .     .  Si 

NON-METALS  ^  Sulphur     ._     .  ^    .  .  .     . 

Bromine Br       Liquid 

Chlorine    ...,.;-.     .     .     .  Cl  Gas 

Fluorine     ..-,....     .     .  Fl 

Hydrogen.     ......     .     .     .  H 

Nitrogen N 

Oxygen O 


A  few  of  the  elements  in  the  above  list  (oxygen,  nitro- 
gen, and  hydrogen)  have  been  studied  in  the  chapters  on 
air  and  water. 

Metals.  —  A  number  of  metals  are  familiar  to  every 
one.  However,  a  few,  such  as  sodium  and  potassium, 


ELEMENTS,   COMPOUNDS,   AND   MIXTURES        251 

are  seen  only  in  the  laboratory.  Each  metal  is  different 
from  the  others  in  certain  characteristic  properties. 
Metals  have  their  own  special  properties  which  enable 
us  to  distinguish  them  as  a  class  quite  readily.  For  ex- 
ample, metals  may  be  melted,  fusibility ;  they  conduct 


Copyright,  1915,  by  Keystone  View  Company. 
FIG.  222.  —  Surface  Mining,  Mesaba  Range,  Minnesota.. 

heat  and  electricity,  conductivity ;  they  may  be  ham- 
mered into  thin  sheets,  malleability ;  tad  the  fresh  sur- 
faces of  metals  have  a  peculiar  luster,.'  , 

Iron.  —  Iron  is  the  most  important  of  all  the  metals. 
It  is  found  in  a  number  of  ores  and  is  sometimes  found 
in  a  free  state  in  igneous  rocks.  Its  abundance  and  its 


252  GENERAL  SCIENCE 

properties  make  it  the  best  metal  for  a  large  variety  of 
uses.      (Figure   222.) 

Cast  iron  contains  from  four  to  five  per  cent  of  carbon 
and  other  impurities.  These  impurities  lower  the  melt- 
ing point  of  cast  iron  to  about  1200°  C.,  and  they  also 
make  the  iron  very  hard  and  brittle. 

Wrought  iron  is  nearly  pure  iron.  To  make  wrought 
iron,  cast  iron  is  remelted  with  another  iron  ore,  hema- 
tite, and  stirred  until  the  impurities  have  been  removed. 
Because  of  its  extreme  toughness,  wrought  iron  is  quite 
valuable.  It  is  used  for  chains,  wire,  bolts,  etc.  It 
melts  at  a  much  higher  temperature  than  cast  iron,  and 
for  this  reason  is  used  for  fire  bars. 

Steel  has  some  carbon  in  it,  but  not  so  much  as  cast 
iron.  It  can  be  tempered  to  different  degrees  of  hardness. 

Copper.  —  Copper  has  a  characteristic  dull  red  color 
when  exposed  to  the  air.  It  melts  at  about  1050°  C.,  is 
a  good  conductor  of  heat  and  electricity,  and  is  quite 
malleable.  It  was  one  of  the  first  metals  used  by  man. 
This  was  because  it  was  found  in  a  free  state  and  did  not 
need  to  be  separated  from  ore  and  also  because  it  is  so 
easily  hammered  into  desired  shapes.  (Figure  223.) 

Copper  is  used  for  electric  wiring,  for  evaporating  pans 
and  some  cooking  utensils,  for  sheathing  ships,  and  for 
places  on  buildings  where  a  metal  is  needed  that  will 
resist  weathering.  Brass  is  an  alloy  of  copper  and  zinc, 
and  bronze  is  an  alloy  of  copper  and  tin. 

Mercury.  —  Most  of  the  mercury  of  commerce  comes 
from  California  and  Spain.  At  ordinary  temperatures  it 
is  a  liquid.  It  solidifies  at  -  40°  C.  and  boils  at  357°  C.- 
It has  a  silvery,  metallic  luster  which  is  not  affected  by 
air  and  water.  Mercury  has  a  number  of  commercial 
uses.  It  is  used  in  thermometers  and  barometers.  In 


ELEMENTS,   COMPOUNDS,   AND   MIXTURES        253 

the  stamp  mills,  pulverized  ores  of  gold  and  silver  are 
mixed  with  water  and  allowed  to  pass  over  layers  of 
mercury.  The  mercury  dissolves  the  particles  of  gold 
and  silver.  Later  they  are  separated  by  distillation. 


Copyright  by  Underwood  &  Underwood,  N.  Y. 

FIG.  223.  —  Copper  Ore  Just  Hoisted  from  the  Shaft,  Calumet  and 
Hecla  Mine,  Michigan. 

Sodium.  —  Sodium  is  a  very  soft  metal  and  may  be 
easily  cut  with  a  knife.  The  surface  of  freshly  cut  sodium 
has  a  luster  resembling  that  of  silver,  but  it  soon  tarnishes 
when  exposed  to  air  or  moisture.  To  keep  sodium  we 
cover  it  with  kerosene,  or  some  oil  which  contains  no 


254  GENERAL  SCIENCE 

oxygen.  Sodium  reacts  vigorously  with  water  to  form 
sodium  hydroxide  and  hydrogen.  The  heat  evolved 
melts  the  sodium  which  forms  into  a  ball  and  floats  on 
the  water. 

Experiment  69.  —  Place  a  small  piece  of  sodium  in  a  wide- 
mouthed  bottle  which  is  two  thirds  full  of  water  and  cover  the 
bottle  with  a  piece  of  glass.  Test  the  gas  formed  in  the  top  of 
the  bottle  with  a  flame.  In  this  experiment  care  should  be  taken 
to  have  the  hands  dry  as  well  as  all  apparatus  used  in  handling 
sodium. 

Salt,  a  compound  of  sodium,  sodium  chloride,  is  found 
in  sea  water  and  in  extensive  deposits  at  Stassfurt  and 
Reichenhall  in  Germany,  in  Cheshire,  England,  and  in 
several  parts  of  the  United  States.  It  is  a  necessary 
article  of  diet.  Salt  may  be  obtained  from  salt  water  by 
evaporating  the  water.  It  crystallizes  in  white  cubes. 
Other  useful  compounds  of  sodium  are  sodium  nitrate 
(Chile  saltpeter)  and  •  sodium  bicarbonate,  which  is 
commonly  known  as  baking  soda. 

Silver.  -  -  The  chief  supply  of  silver  is  obtained  from 
ores  of  lead  and  copper.  Silver  is  mined  extensively  in 
the  western  part  of  the  United  States,  'Mexico,  and 
Australia.  For  silverware  and  coins,  silver  is  alloyed 
with  10  per  cent  of  copper ;  that  is,  they  are  "  900  fine." 
Sterling  silver  is  925  fine  or  it  is  92|  per  cent  pure 
silver.  Articles  may  be  plated  with  silver  by  the  method 
described  under  electroplating  in  Chapter  XI.  Mirrors 
are  silvered  by  cleaning  the  surface  of  the  glass  and  pour- 
ing over  it  a  solution  of  silver  nitrate,  ammonium  hy- 
droxide, and  some  reducing  agent,  such  as  formaldehyde. 
The  film  of  silver  which  adheres  to  the  glass  is  dried  and 
varnished  to  protect  it.  Photographic  plates  and  films 
are  made  by  washing  them  with  an  emulsion  of  silver 


ELEMENTS,   COMPOUNDS,   AND  MIXTURES        255 

bromide  and  gelatine.  The  silver  bromide  is  quite  sen- 
sitive to  light,  and  when  the  plate  is  exposed  and  properly 
developed  a  silver  image  of  the  object  photographed  is 
left  upon  it.  The  "  printing  paper  "  -is  essentially  like 
the  plates.  Some  papers  are  washed  with  a  silver  chlo- 
ride and  white  of  egg  emulsion,  and  others  like  "velox" 
are  rendered  sensitive  to  light  by  being  washed  with  a 
silver  bromide  emulsion. 

Gold.  —  Gold  is  found  in  a  pure  state  in  veins  of 
quartz  in  almost  every  part  of  the  world.  Occasionally 
large  nuggets  of  gold  are  found. 

Since  gold  is  little  affected  by  the  chemical  action  of 
the  air,  water,  and  other  substances,  it  has  come  into 
common  use  for  coins  and  jewelry.  It  is  alloyed  with 
silver  and  copper  to  give  it  hardness.  Twenty-four  carat 
gold  is  pure  gold ;  eighteen  carat  gold  is  three  fourths 
pure ;  and  fourteen  carat  gold  is  ^J  pure.  The  gold 
coins  of  the  United  States  are  ninety  per  cent  gold  and 
ten  per  cent  copper.  Gold  is  the  most  ductile  and  malle- 
able of  metals.  It  melts  at  1075°  C.  It  is  not  dissolved 
by  any  single  acid,  but  a  mixture  of  hydrochloric  and 
nitric  acids  will  dissolve  it. 

Chlorine. -- The  gases,  oxygen,  hydrogen,  and  nitro- 
gen, which  we  have  studied  previously  are  colorless, 
odorless,  and  tasteless  ;  but  chlorine  is  a  green  gas  having 
a  disagreeable  suffocating  odor.  When  breathed,  it  irri- 
tates the  lining  of  the  nose  and  throat.  Chlorine  occurs 
in  a  great  many  compounds,  but  it  is  found  most  abun- 
dantly in  common  salt.  It  is  named  from  chloros,  a  Greek 
word  meaning  green. 

Chlorine  is  a  powerful  bleaching  agent  and  has  a  wide 
commercial  use  for  this  purpose.  Large  quantities  of  it 
are  used  in  making  bleaching  powder,  chloride  of  lime.  It 


256 


GENERAL  SCIENCE 


is  the  bleaching  agent  used  to  bleach  rags  in  the  paper 
mills,  and  to  whiten  cotton  cloth  in  the  cotton  mill. 

Chlorine  may  be  obtained  by  passing  a  current  of 
electricity  through  an  aqueous  solution  of  common  salt. 

Sulphur.  —  A  large  part  of  the  sulphur  used  in  the 
world  comes  from  Sicily  and  Louisiana.  It  occurs  in 
Louisiana  in  a  deposit  about  one  half  mile  in  diameter 


FIG.  224.  —  A  Well  Pumping  Sulphur. 

and  at  a  depth  of  900  feet  (Figure  224).  It  is  a  yellow 
solid  not  soluble  in  water  but  soluble  in  carbon  disulphide. 
If  a  solution  of  sulphur  in  carbon  disulphide  is  evaporated, 
sulphur  crystals  will  be  formed.  The  evaporation  must  be 
carried  on  over  a  steam  bath,  as  carbon  disulphide  is  very 
inflammable. 

Sulphur-  or  brimstone  has  a  number  of  uses.  Sul- 
phur oxide,  which  is  formed  when  sulphur  is  burned  in 
the  air,  will  destroy  disease  germs  and  vermin.  To  fumi- 


ELEMENTS,   COMPOUNDS,  AND  MIXTURES        257 

gate  a  room  with  sulphur,  it  is  only  necessary  to  close 
the  room  and  burn  sulphur  in  it.  Sulphur  is  also  used 
as  a  bleaching  agent  for  those  fabrics  and  materials 
which  would  be  injured  by  chlorine.  The  fumes  from 
sulphur  are  poisonous  and  should  not  be  breathed  in  large 
quantities. 

Carbon.  —  Of  all  the  non-metallic  elements  carbon  is 
the  most  abundant.  There  are  only  three  non-metallic 
elements  which  are  solids  at  ordinary  temperatures  — 
carbon,  phosphorus,  and  sulphur. 

Carbon  appears  in  many  common  forms  in  the  impure 
state,  as  coal,  soot,  or  lampblack,  charcoal  and  graphite, 
or  the  black  lead  of  our  lead  pencils.  It  is  found  in 
considerable  quantities  in  all  vegetable  and  animal  sub- 
stances. When  such  substances  are  burned,  the  black 
carbon  is  exposed  to  view.  When  wood  is  charred,  when 
toast  is  burned,  or  when  meat  is  scorched,  the  black 
which  appears  is  carbon.  If  the  combustion  is  complete, 
the  carbon  disappears  and  only  the  mineral  ash  is  left. 

Except  in  the  case  of  the  diamond,  carbon  is  a  black 
solid.  The  diamond  is  so  different  in  appearance  and 
properties  from  the  other  forms  of  carbon  —  graphite, 
charcoal,  soot,  and  coke  —  that  it  is  hard  to  believe  that  it 
is  the  same  element.  However,  if  these  substances  are 
burned  in  pure  oxygen,  they  all  form  the  same  product, 
carbon  dioxide.  This  proves  conclusively  that  they  are 
the  same  element. 

QUESTIONS 

1.  Give  four  examples  of  physical  change. 
Give  four  examples  of  chemical  change. 

2.  What  is  oxidation  ? 

3.  What  is  an  element?     A  compound?     A  mixture? 

4.  How  do  you  know  iron  to  be  an  element? 


258  GENERAL  SCIENCE 

5.  Why  do  we  paint  iron  building  frames? 

*   6.  Name  ten  of  the  most  useful  elements. 

7.  Name  four  uses  of  cast  iron.     Three  uses  of  wrought  iron. 

8.  How  is  chlorine  used  in  warfare? 

9.  Arrange  iron,  lead,  zinc,  sodium,  gold,  aluminum,  copper, 
silver,  and  platinum  in  order  of  their  densities. 

10.  What  are  some  of  the  commercial  uses  of  gold?     Lead? 
Tin?  Zinc?     Copper?     Sulphur?     Aluminum? 

11.  What  causes  the  hardness  of  razor  steel? 

12.  What  kind  of  iron  would  you  use  for  bicycle  pedals?     Why? 


CHAPTER   XV 
FUELS   AND    CARBON  COMPOUNDS 

Fuels.  —  Fuels  are  materials  used  for  producing  heat. 
They  must  be  capable  of  uniting  with  oxygen  under 
easily  pbtainable  conditions,  with  sufficient  rapidity  to 
insure  the  evolution  of  considerable  heat  energy.  These 
conditions  are  largely  filled  by  carbon  and  its  compounds, 
occurring  as  gases,  liquids,  and  solids. 

f  wood 
Impure  fuels  —  solids      ''„  .    ..    >     .     .     .1  peat 

[  soft  coal 
("  hydrogen 

gases    .     ;     .     ...:;    -hydrocarbons 
carbon 


Nearly  pure  fuels 


liquids 


alcohols 
hydrocarbons 


I*  anthracite  (hard  coal) 
solids    .    .     .     .  •   . .    .  i  Coke 

[  charcoal 

Wood  was  probably  the  first  fuel  used  by  man. 
Peat  came  into  quite  general  use  in  Europe  during  the 
middle  ages  and  is  still  used  to  some  extent  (Figure  225). 
Soft  coal  was  first  used  during  the  fifteenth  century, 
while  gas  and  hard  coal  were  not  used  until  the  first  part 
of  the  nineteenth  century.  Hydrocarbons  in  the  form  of 
gasoline  and  kerosene  and  certain  artificial  gases  were  not 
used  for  fuel  until  the  middle  of  the  nineteenth  century, 

259 


260 


GENERAL  SCIENCE 


and  alcohols  are  just  now  in  the  process  of  being  developed 
as  fuels. 

Wood.  —  Wood  is  a  very  impure  form  of  fuel.     It  con- 
tains water,  resin,  starch,  cellulose,  gum,  oil,  and  mineral 


v  Copyright  by  Underwood  &  Underwood,  N.  Y. 

FIG.  225.  —  Cutting  Peat,  the  Vegetable  Substitute  for  Coal, 
Kiltoom,  Roscommon,  Ireland. 

matter  (ash).  Before  the  wood  can  burn,  the  water 
must  be  evaporated,  and  the  other  substances  contained 
in  the  wood  must  be  raised  to  the  temperatures  at  which 
they  decompose,  yielding  gases  of  a  combustible  nature 
and  charcoal.  A  large  amount  of  heat  is  required  to  do 


FUELS  AND   CARBON   COMPOUNDS 


261 


this.  The  fuel  efficiency  of  wood  depends  upon  the 
relative  amounts  of  combustible  gas  and  carbon  or 
charcoal  furnished.  Hardwood  furnishes  the  most  car- 
bon and  is  therefore  better  for  fuel  than  soft  wood. 

Coal.  —  If  we  look  at  soft  coal  through  a  microscope  we 
find  that  it  consists  of  a  black  mass  of  vegetable  matter, 
such  as  grass,  leaves,  shrubs,  trunks  and  roots  of  trees. 
Because  of  some  change  in  the  earth's  surface,  this  material 
was  covered  with  water  and  mud  and  thus  prevented 
from  decaying.  In  this  condition  the  mass  slowly  changes 
from  the  carbon  compounds  to  pure  carbon.  The  fuel 
value  of  the  coal  depends  upon  the  extent  to  which  this 
change  has  taken  place.  Peat  must  be  dried  before  it 
will  burn.  Bituminous,  or  soft  coal  still  contains  many 
carbon  compounds  and  burns  with  a  long  yellow  flame. 
Hard  coal,  or  anthracite,  in  which  the  carbon  compounds 
have  been  changed  to  nearly  pure  carbon,  has  no  flame 
and  can  be  burned  only  in  a  strong  draft. 

Experiment  70.  —  Charcoal  and  Coke.  —  Fill  a  long  test  tube  one 
third  full  of  dry  sawdust  and  heat  it  slowly.  Test  the  gases  evolved 
by  bringing  a  lighted  splinter  to  the  mouth  of  the  test  tube. 

When  wood  is 
heated  in  a  retort 
from  which  the  air 
is  excluded,  several 
products  result : 
inflammable  gases 
are  driven  off,  tarry 
liquids  appear  in 
the  retort,  and  the  wood  changes  to  a  porous  black  solid 
(Figure  226).  In  the  manufacture  of  charcoal  on  a  large 
scale  the  wood  is  heated  in  a  large  iron  cylinder.  The 
valuable  liquid  products  are  led  away  by  tubes.  Among 


FIG.  226.  —  Wood  Arranged  for  Burning  into 
Charcoal. 


262 


GENERAL  SCIENCE 


these  products  are  wood  alcohol  and  acetic  acid.  Char- 
coal made  at  a  low  temperature  is  very  inflammable  and 
burns  with  an  intense  heat.  It  is  very  porous  and  is  able 
to  absorb  many  times  its  own  volume  of  certain  gases. 

Coke  bears  the  same  relation  to  soft  coal  that  charcoal 
does  to  wood.  Coal  is  heated  in  a  retort  from  which  air 
has  been  excluded,  until  everything  that  has  been  driven 
off  by  heat  has  escaped.  Other  valuable  products  of  the 
process  are  illuminating  gas,  ammonia  water,  benzene, 

creosote,  carbolic  acid,  pitch,  and 
tar-camphor. 

Charcoal  and  coke  are  used  as 
fuels  and  in  the  reduction  of  the 
ores  of  iron  and  other  metals. 
The  oxide  of  a  metal  when  heated 
with  carbon  decomposes ;  the 
oxygen  unites  with  the  carbon 
and  releases  the  metal. 
,  Hydrocarbons.  —  A  compound 
of  carbon  and  hydrogen  is  called 
a  hydrocarbon.  There  are  a 
number  of  hydrocarbons.  Marsh 
gas,  composed  of  one  atom  of 
carbon  and  four  atoms  of  hydro- 
gen, is  formed  in  the  rotting  vegetable  matter  at  the 
bottom  of  a  marshy  pool.  Figure  227  shows  a  method 
of  collecting  this  gas.  It  is  a  colorless,  combustible  gas 
and  burns  with  a  pale  blue  flame.  In  mines  this  gas  is 
called  fire  damp. 

In  the  manufacture  of  coke  a  number  of  gases  are 
produced.  The  coal  gas  which  we  use  for  heating  and 
lighting  is  about  one  third  marsh  gas  (methane),  forty- 
five  per  cent  hydrogen,  some  carbon  monoxide,  and  nitro- 


FIG.  227.  —  Collecting  Marsh 
Gas. 


FUELS  AND   CARBON   COMPOUNDS 


263 


gen,    and   a   small   percentage   of   other   hydrocarbons : 
acetylene,  ethylene,  and  benzene. 

Natural  gas  is  largely  used  for  heating  and  lighting 
purposes  in  certain  localities  and  is  reached  by  drilling. 
Natural  gas  consists  mainly  of  hydrogen  and  marsh  gas 
and  is  excellent  for  heating  purposes.  Since  it  burns 
with  almost  no  flame,  it  has  little  illuminating  power. 


rtirr 


U.  S.  Geological  Survey. 
FIG.  228.  —  Oil  Derricks,  Beaumont,  Texas. 

For  lighting  purposes  it  is  used  to  heat  a  mantle  to  in- 
candescence. 

Petroleum.  —  Petroleum  is  a  dark,  oily  liquid  obtained 
from  oil  wells  in  certain  localities,  especially  in  Pennsyl- 
vania, Ohio,  Texas,  California,  and  near  Baku  in  Russia 
(Figure  228).  All  petroleums  are  mixtures  of  hydrocar- 
bons. Nearly  all  the  petroleum  produced  is  refined.  The 


264 


GENERAL  SCIENCE 


refining  of  petroleum  is  essentially  a  process  of  distillation 
in  which  the  crude  oil  is  separated  into  a  number  of  frac- 
tions which  have  different  boiling  points  and  compositions. 
Some  of  the  products  obtained  are  petroleum,  ether,  gaso- 
line, naphtha,  benzene,  kerosene,  paraffine,  vaseline,  and 
petroleum  jelly.  Of  this  list  gasoline,  naphtha,  benzene, 
and  kerosene  are  quite  commonly  used  as  fuels. 

Flash  Test.  —  Half  fill  a  200  cc.  beaker  with  kerosene, 
and  place  over  water  (Figure  229).  Stir  constantly  with 
an  accurate  Fahrenheit  thermometer 
and  heat  slowly  until  a  small  flame  held 
over  the  mouth  of  the  beaker  causes  a 
slight  explosion  and  a  blue  flame.  This 
is  the  flashing  point  and  should  not  be 
lower  than  150°  Fahrenheit.  A  lower 
flashing  point  indicates  the  presence  of 
hydrocarbons  which  have  a  low  boiling 
point,  such  as  gasoline,  and  that  the 
kerosene  is  not  safe  to  use  in  lamps. 

Alcohols.  —  It  is  quite  probable  that 
alcohol  will  come  into  common  use  as  a 
fuel  in  the  event  of  a  scarcity  of  petro- 
leum. It  is  composed  of  carbon,  hydrogen,  and  oxygen, 
and  has  a  high  fuel  value.  Denatured  alcohol  is  simply 
grain  alcohol  to  which  has  been  added  a  small  quantity 
of  wood  alcohol  and  benzene. 

Sources  of  Fire.  -  -  The  origin  of  fire  furnished  the  basis 
of  a  number  of  mythological  tales.  Just  when  fire  was 
discovered  is  not  known,  for  it  was  long  before  the  period 
of  authentic  history.  Probably  friction  was  the  first 
method  used  by  primitive  peoples  to  raise  the  temperature 
of  dry  wood  to  the  kindling  temperature.  A  hundred 
years  ago  a  spark  of  fire  was  obtained  by  striking  a 


FIG.  229.  — Method 
of  Obtaining  the  Flash- 
ing Point  of  Kerosene. 


FUELS  AND   CARBON  COMPOUNDS 


265 


piece  of  flint  with  steel.     This  spark  was  caught  on  some 
tinder  and  carefully  fanned  into  a  blaze. 

The  friction  match,  which  came  into  use  about  1827,  was 
a  very  crude  invention  if  compared  with  the  modern 
safety  match,  but  it  was  far  superior  to  the  flint  and  steel. 
The  first  matches  were  made  of  sulphur  mixed  with  a 
little  potassium  chlorate  and  antimony  sulphide.  This 
mixture  was  used  to  coat  the  end  of  a  small  wooden  stick. 
When  the  match  was  rubbed  over  a  rough  surface,  the 


FIG.  230.  —  An  Old-fashioned  Fireplace. 

friction  produced  enough  heat  to  cause  the  sulphur  to 
unite  with  the  oxygen  of  the  potassium  chlorate,  and  the 
burning  sulphur  would  ignite  the  wooden  stick.  These 
matches  burned  with  a  very  bad  odor.  The  match  has 
been  much  improved  in  recent  years.  The  safety  match 
is  now  in  quite  common  use,  because  it  is  less  dangerous 
to  use  and  to  manufacture.  Red  phosphorus  is  used  on 
the  safety  match  instead  of  the  more  active  yellow  phos- 
phorus and  is  also  placed  on  the  striking  surface.  The  tip 
of  the  match  contains  antimony  sulphide  and  some  oxidiz- 
ing substance,  such  as  potassium  chlorate  or  oxide  of  lead. 


266 


GENERAL  SCIENCE 


Apparatus  for  Utilizing  Fuels.  —  Most  of  the  modern 
fireplaces  are  built  more  for  ornament  than  for  use,  but 
it  has  been  less  than  a  hundred  years  since  the  fireplace 
was  the  means  of  heating  the  home  and  cooking  the  food 
(Figure  230).  Of  course  the  waste  of  heat  in  the  fire- 
place was  large,  but  it  was  an  excellent  ventilator  and 
furnished  a  cheer  that  is  absent  in  the  modern  methods  of 
heating. 

Stoves.  -  -  There  have  been  invented  numerous  stoves 
which  are  designed  to  utilize  fuels  more  economically 
and  more  conveniently  than  the  fireplace.  Cooking 

stoves  which  burn  coal 
and  wood  are  so  con- 
structed that  the  heated 
gases  pass  in  a  round- 
about way  to  the  flues, 
thus  heating  the  ovens. 
Gas  stoves  usually  have 
special  heaters  for  the 
ovens. 

Gasoline  stoves  are 
really  gas  stoves.  To 
light  a  gasoline  stove  we  must  heat  the  vaporizer. 
This  is  done  by  burning  some  gasoline  in  a  cup  be- 
neath it.  When  the  gasoline  is  allowed  to  enter  the 
heated  vaporizer,  it  is  changed  to  the  gaseous  form  and 
mixed  with  the  air  which  is  drawn  in  by  the  force 
of  the  current  of  gasoline  vapor.  This  mixture  burns 
with  a  very  hot  flame  and  is  much  used  for  cooking 
purposes. 

Electric  stoves  are  now  being  used  in  many  ways  for 
heating  and  cooking  and  have  many  advantages.  We 
now  have  electric  toasters,  coffee  percolators,  flatirons, 


FIG.  231.  — Electric  Flatiron. 


FUELS  AND  CARBON  COMPOUNDS 


267 


FIG.  232.  —  Electric  Grill. 


hot-water  bags,  and  numerous  other  appliances  which 
utilize  a  small  amount  of  current  to  apply  heat  exactly 
where  it  is  needed  (Figures  231,  232,  233). 

Carbon  Dioxide.  —  Car- 
bon dioxide  is  occasionally 
found  issuing  froni  the 
ground,  especially  in  vol- 
canic regions,  and  dis- 
solved in  the  water  of 
certain  springs.  The 
charged  water  of  the  soda 
fountains  is  simply  water 
in  which  a  large  amount  of 
carbon  dioxide  has  been 
dissolved  under  pressure.  Carbon  dioxide  is  always 
formed  when  carbon  or  carbon  compounds  burn  in  air 
or  oxygen.  A  small  amount  of  carbon  dioxide  is  always 

present  in  the  air,  since  it 
is  produced  when  any  sub- 
stance is  burned,  by  the 
decay  of  all  vegetable  and 
animal  matter,  and  by  the 
breathing  of  plants  and  ani- 
mals. 

Preparation  of  Carbon 
Dioxide.  —  Place  a  few 
pieces  of  marble  or  lime- 
stone in  a  bottle  (Figure 
234)  and  pour  over  them 
a  dilute  solution  of  hydrochloric  acid.  The  gas  formed 
is  carbon  dioxide.  The  gas  may  be  collected  by  down- 
ward displacement  of  air,  or  over  water  as  we  collected 
oxygen. 


FIG.  233.  —  Electric  Toaster. 


268 


GENERAL  SCIENCE 


FIG.    234.  —  Preparation    and 
Collection  of  Carbon  Dioxide. 


Test  the  carbon  dioxide  as  you  tested  oxygen  and  hydro- 
gen to  determine  whether  or  not  it  will  burn  and  support 
combustion.  Pass  some  of  the  gas  through  limewater, 
which  is  simply  'a  clear  solution  of  slaked  lime  in  water. 

The  white  precipitate  formed  is 
calcium  carbonate.  Test  your 
breath  in  the  same  way.  What 
does  this  prove  about  the  air 
which  is  expelled  from  the  lungs 
(Figure  235)? 

Properties  and  Uses  of  Carbon 
Dioxide.  —  Since  we  can  collect 
carbon  dioxide  by  the  downward 
displacement  of  air,  we  would 
infer  that  it  is  heavier  than  air  and  that  it  diffuses  quite 
slowly.  It  is  one  and  one  half  times  as  heavy  as  air. 
Since  it  does  not  support  combustion,  it  is  used  in  chemi- 
cal fire  extinguishers.  Figure  236  shows  such  an  extin- 
guisher. The  tank  contains  soda. 
When  the  extinguisher  is  inverted, 
the  acid  pours  from  the  bottle 
and  the  large  quantity  of  carbon 
dioxide  made  passes  out  through 
the  nozzle.  The  heavy  gas  ex- 
cludes the  oxygen  from  the  fire 
and  thus  extinguishes  it. 

Carbon  dioxide  does  not  sup- 
port respiration  and  if  breathed 
in  any  considerable  quantity  will  produce  death,  not 
because  it  is  poisonous  but  because  the  necessary  oxygen 
is  excluded. 

Because  of  its  density  carbon  dioxide  is  often  found  at 
the  bottom  of  empty  wells,  and  in  abandoned  mines  and 


Suction 


FIG.  235. 


FUELS  AND  CARBON  COMPOUNDS 


269 


cellars,  where  it  is  sometimes  called  "  choke  damp." 
Before  entering  such  places  it  will  be  well  to  test  for  the 
presence  of  carbon  dioxide  by  lowering  a  lighted  candle 
into  the  cavity. 

Under  a  pressure  of  735  pounds  to  the  square  inch  the 
gas  may  be  liquefied  at  ordinary  temperatures.  The 
liquefied  carbon  dioxide  is  kept  in  strong  cylinders  from 
which  it  is  taken  as  needed  for  use,  as 
in  soda  fountains,  by  means  of  a  valve. 

Fermentation. -- The  fresh  juice  of 
certain  fruits  is  sweet  on  account  of  the 
presence  of  sugar.  If  grape  juice  is 
heated  and  sealed  up  while  hot,  it  will 
remain  sweet,  but  when  allowed  to  stand 
exposed  to  the  air  it  ferments.  Bubbles 
of  gas  escape  and  the  sweet  taste  is 
replaced  by  the  mild  alcoholic  taste  of  J[™'  2^0~^ Dthe 
wine.  The  fermentation  is  caused  by  a  Cross  Section  of  a  Fire 

i  n    j  mu  Extinguisher. 

plant  called  yeast.     The  spores  or  yeast 
seeds  fall  into  the  juice  and  sprout,  producing  innumerable 
yeast  plants.     As  these  plants  grow  they  change  the  sugar 
to  alcohol  and  carbon  dioxide.     The  gas  may  be  tested 
by  passing  it  over  limewater. 

When  yeast  is  put  in  a  mixture  of  flour,  water,  and 
sugar  (dough) ,  the  bubbles  of  carbon  dioxide .  cause  the 
bread  to  rise.  The  action  of  the  yeast  is  arrested  by  the 
intense  heat  of  baking. 

For  raising  certain  pastries,  an  artificial  source  of 
carbon  dioxide  is  often  used.  This  may  be  ordinary 
baking  soda  (sodium  carbonate)  used  with  sour  milk, 
or  baking  powder.  When  baking  soda  and  sour  milk 
are  used,  the  lactic  acid  of  milk  reacts  with  the  baking 
soda  in  the  same  way  that  acid  reacts  with  the  marble, 


270  GENERAL  SCIENCE 

liberating  carbon  dioxide,  which  is  caught  by  the  sticky 
mass  of  dough  and  gives  to  the  dough  a  porous  structure. 

Baking  powder  contains  soda  and  cream  of  tartar. 
When  the  powder  is  put  in  moist  dough,  the  cream  of 
tartar  acts  as  an  acid  on  the  soda,  and  carbon  dioxide  is 
formed.  Acid  phosphate  baking  powders  contain  acid 
calcium  phosphate  instead  of  cream,  of  tartar. 

Carbonates.  —  Other  common  and  useful  carbonates 
besides  sodium  carbonate  are  calcium  carbonate  and 
potassium  carbonate. 

Limestone  is  found  in  large  quantities  in  the  earth. 
When  it  is  heated  to  a  high  temperature,  it  is  decomposed 
into  lime  and  carbon  dioxide.  Lime  is  used  in  many  ways 
as  the  binding  material  in  mortar  and  plaster. 

Potassium  carbonate  is  a  white  powder  similar  to  sodium 
carbonate.  Wood  ashes  were  for  many  years  the  sole 
source  of  it.  This  is  the  reason  it  is  called  "  potash," 
from  which  the  name  potassium  was.  derived. 

Potassium  carbonate  was  once  used  in  making  soaps, 
but  later  methods  use  the  cheaper  sodium  carbonate. 

QUESTIONS 

1.  What  fuel  is  most  used  in  your  city?     Why? 

2.  Why  is  dry  wood  a  better  fuel  than  green  wood? 

3.  Why  is  hard  pine  a  good  fuel  wood? 

4.  The  flashing  point  of  a  sample  of  kerosene  is  150°  Fahrenheit. 
What  will  it  be  Centigrade? 

5.  Why  does  the  carbon  dioxide  in  soda  water  come  to  the 
surface  when  the  water  is  drawn  ? 

6.  How  can  you  prove  that  carbon  dioxide  will  not  support 
combustion? 

7.  Should   the  ventilator  in  a   hot-air  system   of   heating   be 
placed  at  the  top  or  bottom  of  a  room?     Why? 

8.  How  are  the  flues  in  a  cook  stove  arranged  to  provide  for 
heating  the  oven? 


FUELS  AND   CARBON   COMPOUNDS  271 

9.    What  kind  of  a  stove  does  alcohol  require? 

10.  Can  alcohol  be  vaporized  and  burned  like  gasoline  vapor? 

11.  What  "  cautions  "  should  be  observed  in  Using  a  gasoline 
stove? 

12.  Is  electricity  an  efficient  source  of  heat ?     Why? 

13.  What  is  the  price  of  artificial  gas' in  your  city?      Of  elec- 
tricity? 

14.  What  are  the  advantages  of  gas  over  coal  as  a  fuel  for  the 
cook  stove? 

15.  Name  three  uses  of  carbon  dioxide. 

16.  When  acid  (hydrochloric  acid)  is  poured  on  calcium  car- 
bonate, what  products  are  formed  ? 

17.  What  is  the  purpose  of  raising  dough? 

18.  When  an  explosion  of  "  fire  damp  "  occurs  in  a  mine,  "choke 
damp  "  is  formed.     Explain  how. 

19.  What  causes  cider  to  "  work  "? 


CHAPTER  XVI 
COMMON   COMPOUNDS   OF   OTHER   ELEMENTS 

Classes  of  Compounds.  —  In  this  chapter  we  shall  deal 
only  with  a  few  classes  of  compounds  whose  names  are 
in  quite  common  use.  We  have  already  used  the  terms 
oxide  and  acid  a  number  of  times  in  this  book.  These 
are  two  of  the  four  large  classes  of  compounds.  The 
other  two  are  bases  and  salts. 

Oxides.  —  Because  of  its  importance  we  are  accustomed 
in  our  preliminary  study  of  oxygen  to  think  that  most  of 
it  is  in  the  air,  but  we  soon  learn  that  this  is  not  the  case. 
Eight  ninths  of  the  weight  of  water  is  oxygen,  but  even 
water  contains  but  a  small  part  of  the  total  amount  of 
oxygen  in  the  earth.  Water  is  an  oxide  as  is  carbon 
dioxide.  Oxygen  unites  with  many  elements  to  form 
oxides. 

Acids.  —  An  acid  is  a  hydrogen  compound  whose  dilute 
water  solution  usually  has  a  sour  taste.  It  turns  a  blue 
litmus  solution  red.  Litmus  is  a  blue  dye  which  is  ob- 
tained from  a  kind  of  moss.  It  readily  dissolves  in  water, 
and  when  a  drop  of  acid  is  added  to  the  resulting  blue 
liquid,  the  color  changes  to  red. 

A  number  of  acids  react  chemically  with  metals,  giving 
off  hydrogen.  For  example,  when  hydrochloric  acid  and 
zinc  are  brought  together,  zinc  chloride  is  formed  and  large 
quantities  of  hydrogen  are  produced.  Copper  vessels 
should  not  be  used  for  cooking  foods  which  contain  acids, 
even  though  they  may  be  very  inactive  acids,  since 

272 


COMMON  COMPOUNDS   OF  OTHER  ELEMENTS     273 


FERMENTED  APPLE  JUICE 


poisonous  compounds  of  copper  may  be  formed.  The 
most  common  acids  are  sulphuric,  hydrochloric,  and 
nitric.  These  are  called  inorganic  or  mineral  acids,  and 
are  manufactured  in  large  quantities  for  commercial  uses. 
Sulphuric  acid  is  quite  cheap  and  is  used  in  the  manu- 
facture of  other  acids.  Hydrochloric  acid  contains 
hydrogen  and  chlorine  and  is  made  by  the  action  of  sul- 
phuric acid  on  salt  (sodium  chloride) . 

Another  large  class  of  acids  is  formed  in  the  juices  of 
fruit  and  vegetables.  Among  these  are  acetic  acid, 
citric  acid,  and  tartaric  acid. 
(All  of  these  acids  contain 
carbon,  hydrogen,  and  oxygen.) 
They  are  called  organic  acids. 

When  sweet  fruit  juices  fer- 
ment, their  sugar  is  changed 
to  alcohol  and  carbon  dioxide 
by  the  yeast  plants.  If  the 
alcohol  thus  formed  comes  into 
contact  with  air,  it  changes  to 
vinegar.  While  this  change 

from  alcohol  to  vinegar  is  going  on  the  liquid  contains 
numerous  small  organisms  called  acetic  acid  bacteria.  The 
large  numbers  of  these  bacteria  form  the  characteristic 
mold  known  as  "  mother  of  vinegar."  The  sour  taste  of 
vinegar  is  due  to  the  acetic  acid  present.  In  the  vinegar 
sold  for  table  purposes  the  amount  of  acetic  acid  is  usually 
not  more  than  four  or  five  per  cent.  In  the  formation  of 
vinegar  the  alcohol  is  really  oxidized  to  acetic  acid.  This 
action  is  usually  slow,  but  may  be  hastened  by  the  quick 
vinegar  process.  This  is  an  arrangement  whereby  fer- 
mented apple  juice  is  allowed  to  drip  slowly  through  beech- 
wood  shavings  which  have  been  inoculated  with  acetic  acid 


FIG.  237. 


274  GENERAL  SCIENCE 

bacteria  by  previously  wetting  them  with  vinegar.  The 
shavings  are  held  in  a  barrel  (Figure  237)  having  a  number 
of  holes  cut  in  it  to  admit  a  plentiful  supply  of  air.  The 
change  from  alcohol  to  vinegar  in  such  an  apparatus  takes 
place  in  a  few  minutes. 

Uses  of  Acids.  —  Acids  have  many  commercial  uses. 
Shortly  after  the  great  European  war  broke  out  the  prices 
of  inorganic  acids  rose  perceptibly.  Both  nitric  and 
sulphuric  acids  are  used  in  the  manufacture  of  many 
high  explosives  such  as  nitro-glycerine,  nitro-cellulose, 
and  guncotton. 

In  addition  to  its  many  direct  commercial  uses,  sul- 
phuric acid  is  used  in  the  manufacture  of  other  acids. 
With  the  present  high  prices,  all  the  old  sulphuric  acid 
plants,  even  those  using  obsolete  methods  of  manufac- 
ture, have  been  placed  in  operation  and  have  proved 
very  profitable.  The  world's  annual  production  of  sul- 
phuric acid  is  several  million  tons.  Hydrochloric  acid  is 
now  made  on  a  large  scale  by  the  action  of  sulphuric  acid 
on  Chile  saltpeter. 

Alkalies  and  Bases.  —  A  base  is  a  substance  which  has 
a  number  of  properties  just  the  opposites  of  the  properties 
of  acids.  Their  solutions  reverse  the  color  changes  pro- 
duced by  acids  on  sensitive  dyestuffs.  Litmus  paper  or 
litmus  solutions  which  have  been  colored  red  by  acids  are 
changed  back  to  blue  by  basic  solutions.  Soluble  bases 
have  a  bitter  taste  quite  different  from  the  sour  taste  of 
acids. 

Common  bases  are  sodium  hydroxide  (caustic  soda), 
potassium  hydroxide  (caustic  potash),  ammonium  hy- 
droxide, and  calcium  hydroxide.  It  will  be  noticed  that 
the  chemical  term  hydroxide  occurs  in  each  of  the  above 
names.  This  means  that  oxygen  and  hydrogen  are 


COMMON   COMPOUNDS  OF  OTHER  ELEMENTS      275 

combined  with  the  different  substances  —  sodium,  potas- 
sium, ammonium,  and  calcium  to  form  the  base.  The 
name  alkalies  is  commonly  applied  to  the  first  two  bases 
mentioned  above.  Alkalies  are  simply  the  more  soluble 
members  of  the  class  of  substances  called  bases.  Any 
basic  reaction  may  be  called  an  alkaline  reaction.  Strong 
alkaline  solutions  are  "  soapy  "  to  the  touch.  Because 
of  their  action  on  grease  and  fats,  alkalies  are  used  in 
the  manufacture  of  soaps,  for  cleaning,  and  for  flushing 
partially  clogged  waste  pipes  leading  from  sinks. 

Salts.  —  When  an  acid  and  a  base  are  brought  together 
in  the  right  proportions,  the  characteristic  properties  of 
each  disappear.  The  hydrogen  and  the  oxygen  of  the  base 
unite  with  the  hydrogen  of  the  acid  to  form  water,  while 
the  residues  of  both  unite  to  form  a  salt.  For  example  : 

Sodium  hydroxide,  a  compound  of  sodium,  hydrogen,  and  oxygen, 

reacts  with 
hydrochloric    acid,    a    compound    of     hydrogen    and    chlorine, 

to  give 
water  and  common  salt  (sodium  chloride). 

Experiment  71.  —  Add  some  hydrochloric  acid  to  a  water  solu- 
tion of  litmus.  Now  add  sodium  hydroxide  solution  drop  by  drop 
until  the  red  color  disappears,  leaving  the  solution  white.  The 
acid  and  the  hydroxide  have  neutralized  each  other.  Evaporate 
the  solution  to  dryness  and  there  will  be  a  residue  of  white  crystals, 
the  properties  of  which  show  it  to  be  common  salt. 

Uses  of  Salts.  -  -  There  are  so  many  different  salts  that 
a  thorough  discussion  of  their  uses  would  involve  the 
whole  subject  of  chemistry.  However,  a  few  common 
salts  and  their  uses  may  be  mentioned  with  profit. 

Copper  sulphate,  "•  blue  vitriol,"  is  a  blue  salt  having 
a  number  of  uses.  It  is  used  in  the  gravity  batteries  of 
the  telegraph  systems.  The  farmer  has  also  discovered 


276  GENERAL  SCIENCE 

a  number  of  uses  for  copper  sulphate.  For  the  preven- 
tion of  "  smut  "  in  wheat  the  seeds  are  wet  with  a  weak 
solution  of  it  before  sowing. 

"  Bordeaux  mixture,"  composed  of  a  mixture  of  copper 
sulphate  and  lime  in  water,  is  widely  used  as  a  fungicide ; 
other  sulphates  are  zinc  sulphate,  "  white  vitriol  "  ;  iron 
sulphate,  "  copperas  "  or  "  green  vitriol  "  ;  potassium 
sulphate,  used  as  a  fertilizer  for  plants;  magnesium 
sulphate,  "  Epsom  Salt  " ;  and  ammonium  sulphate, 
which  is  used  in  large  quantities  as  a  fertilizer  to  supply 
nitrogen  to  crops.  The  use  of  sodium  chloride  is  well 
known. 

Silver  chloride  and  silver  bromide  are  used  in  photog- 
raphy, since  they  are  chemically  affected  by  light. 

Silver  nitrate  is  used  in  the  manufacture  of  photo- 
graphic films  and  plates  to  produce  the  sensitive  chloride 
of  silver.  It  is  also  used  in  the  indelible  marking  of 
linens,  since  the  organic  matter  of  cloth  or  skin  converts 
the  nitrate  to  silver  and  produces  the  black  stain. 

Ammonium  nitrate  is  used  in  the  manufacture  of  ex- 
plosives. 

Calcium  phosphate,  which  occurs  as  phosphate  rock  in 
South  Carolina,  Tennessee,  Florida,  Idaho,  Utah,  Mon- 
tana, and  Wyoming,  is  used  in  the  manufacture  of  fer- 
tilizers. More  than  a  million  tons  of  this  rock  are  being 
used  each  year.  To  render  the  calcium  phosphate  more 
active  it  is  treated  with  sulphuric  acid,  which  converts 
the  whole  mass  into  the  very  soluble  calcium-hydrogen 
phosphate,  and  calcium  sulphate.  The  mixture  is  sold 
for  fertilizer  as  "  superphosphate." 

Electrolytes. — The  process  of  decomposing  a  compound 
substance  by  means  of  an  electric  current  is  called  elec- 
trolysis. The  substance  decomposed  is  called  an  electro- 


COMMON  COMPOUNDS  OF  OTHER  ELEMENTS      277 


lyte.  Water  solutions  of  acids,  bases,  and  salts  are 
all  conductors  of  electricity;  and  in  each  case  the  sub- 
stance in  solution  (solute)  is  decomposed  by  the  electric 
current.  The  decomposition  always  results  in  two  parts, 
one  of  which  is  carried  to  the  positive  electrode  while  the 
other  is  carried  to  the  negative  electrode.  For  example, 
the  electrolysis  of  acids  always  gives  hydrogen  at  the 
negative  electrode  and  the  remainder  of  the  compound 
at  the  positive  electrode.  Acids,  bases,  and  salts  are  the 
only  substances  which  in  water  solutions  are  electrolytes. 

A  simple  apparatus  for  showing  the  conductivity  of 
electrolytes  is  shown  in  Figure  238.  The  lamp,  which 
should  be  a  small  one, 
is  placed  in  series  with 
the  platinum  electrodes. 
When  a  conductor  of 
electricity  is  placed  in  the 
jar  and  the  connection  is 
made  with  a  battery  of 
sufficient  size,  the  lamp 
will  glow.  If  only  a  few 
cells  are  available,  a  telephone  receiver  may  be  substi- 
tuted for  the  lamp.  When  the  circuit  is  made  or  broken, 
the  receiver  will  click.  In  this  way  test  the  conductivity 
of  dry  salts. 

Analysis  of  Chemicals.  —  It  is  often  quite  important 
to  determine  just  what  elements  or  compounds  are  present 
in  certain  substances.  The  agricultural  chemist  analyzes 
soils  to  determine  what  crops  they  are  best  suited  to, 
and  what  fertilizers  are  needed.  Health  officers  analyze 
foods  of  all  sorts  to  determine  their  food  value  and  also 
to  guard  the  public  against  harmful  substances  which 
are  occasionally  found  in  them.  The  geologist  analyzes 


FIG.  238. 


278  GENERAL  SCIENCE 

rocks  and  ores  to  determine  their  composition  and  value. 
To-day  nearly  all  mining  companies  and  manufacturing 
companies  maintain  their  own  laboratories  for  examining 
the  materials  in  which  they  are  interested. 

To  "  test  "  a  substance  for  the  purpose  of  rinding  out 
whether  a  certain  element  or  compound  is  present  or  not 
we  simply  make  an  examination  of  the  substance,  neglect- 
ing so  far  as  possible  other  elements  or  compounds  present. 
No  two  substances  have  exactly  the  same  properties,  and 
so  "  tests  "  may  be  devised  for  distinguishing  any  certain 
substance. 

We  may  test  for  acids  as  a  class  by  using  litmus  paper 
or  litmus  solution,  but  we  shall  not  be  able  by  this  test 
to  tell  whether  the  acid  present  is  hydrochloric,  sulphuric, 
or  any  one  of  a  number  of  other  acids. 

In  testing  a  salt  we  need  to  determine  :  (a)  what  metal 
is  present  and  (b)  what  acid  was  used  in  producing  it.  If 
sulphuric  acid  was  used,  we  call  the  salt  a  sulphate ;  if 
hydrochloric  acid  was  used,  a  chloride ;  if  nitric  acid  was 
used,  a  nitrate ;  if  phosphoric  acid  was  used,  a  phosphate  ; 
and  so  on. 

Iron.  —  If  solutions  containing  iron  salts  are  heated 
with  a  little  concentrated  nitric  acid  and  boiled  for  a  few 
minutes,  and  a  few  drops  of  potassium  thiocyanate  are 
added,  a  beautiful  blood-red  solution  results. 

Copper.  —  If  copper  is  present  in  a  solution,  the  addition 
of  ammonia  gives  a  deep  blue  color. 

Sodium.  —  Sodium  salts  give  a  bright  yellow  color  when 
held  in  a  colorless  gas  flame. 

Sulphates.  —  To  test  for  sulphate  salts,  we  add  dilute 
nitric  acid  to  a  water  solution  of  the  salt  and  then  add  a 
few  drops  of  barium  chloride  solution.  If  the  salt  is  a 
sulphate,  there  will  be  a  white  precipitate  formed. 


COMMON   COMPOUNDS   OF   OTHER   ELEMENTS     279 

Chlorides.  -  -  To  test  for  a  chloride,  add  a  few  drops  of 
nitric  acid  to  a  water  solution  of  the  salt  and  then  add  a 
few  drops  of  silver  nitrate  solution.  If  the  salt  used  is 
a  chloride,  there  will  be  a  white  precipitate  of  silver  chlo- 
ride formed.  When  exposed  to  the  sunlight,  this  precipi- 
tate turns  black. 

QUESTIONS 

1.  Name  four  substances  which  are  not  combustible. 

2.  Why  does  a  substance  which   is   completely  oxidized   not 
burn? 

3.  Which  is  the  most  important  acid?     Why? 

4.  In  case  an  acid  is  spilled  on  clothing,  what  would  you  use 
to  neutralize  the  acid? 

5.  Sometimes  solids  will  show  an  acid  reaction.     What  com- 
mon substance  would  you  suggest  to  neutralize  the  acid  ? 

6.  Common  salt  is  a  compound  of  sodium  and  chlorine.     Sug- 
gest a  way  to  separate  the  sodium  from  the  chlorine. 


CHAPTER  XVII 
SOILS 

THE  soil  is  not  unlike  many  other  things  of  this  world  ; 
it  needs  to  be  understood  in  order  to  be  appreciated. 
Contrary  to  the  opinion  quite  commonly  held,  soil  is  not 
dirt  in  the  sense  of  the  word  that  it  is  something  to  be 


U.  S.  Geological  Survey. 
FIG.  239.  —  Igneous  Rock. 

Characteristic  lava  flow,  Kilauea,  Hawaii. 

avoided,  .  Nearly  everything  that  we  eat  and  wear  comes 
either  directly  or  indirectly  from  the  soil.  We  are  de- 
pendent upon  the  soil  for  our  very  existence,  and  we  should 
have  a  wholesome  respect  for  the  tillers  of  the  soil.  With 

280 


SOILS  281 

the  development  of  the  science  of  agriculture  a  man  is 
able  to  produce  much  more  on  an  acre  of  ground  than 
formerly.  The  surplus  that  he  does  not  need  for  his  own 
uses  is  exchanged  for  the  manufactured  products  of  his 
city  brother,  and  both  the  manufacturer  and  the  farmer 
profit  thereby. 

The  Crust  of  the  Earth.  -  -  The  crust  of  the  earth  varies 
greatly  in  composition.     Many  different   kinds  of  rocks 


FIG.  240.  —  Sedimentary  Rock. 
Horizontal  strata  near  Quebec,  Canada,  showing  layers  of  sediment. 

are  found  on  or  near  the  surface  of  the  earth.  These  are 
covered  with  a  variety  of  soils,  the  soil  usually  containing 
in  each  case  the  same  elements  and  compounds  as  the 
rocks  below  it. 

The  rocks  of  the  earth's  crust  are  divided  into  three 
classes :  igneous,  sedimentary,  and  metamorphic,  in 
accordance  with  the  manner  of  their  formation. 

Igneous  rocks  are  those  which  at  some  time  in  their 


282 


GENERAL  SCIENCE 


history  have  been  solidified  from  a  melted  condition.  If 
on  solidifying  the  cooling  has  been  slow,  these  rocks  will 
have  a  crystalline  structure  such  as  is  found  in  marble. 
Lava  is  a  form  of  igneous  rock  (Figure  239). 

Sedimentary  rocks  are  those  formed  by  the  deposition 
of  sand,  gravel,  clay,  and  other  materials,  by  water.    The 


U.  S.  Geological  Survey. 
FIG.  241.  —  Sedimentary  Rock. 

Showing  a  fault  in  rock  formation,  Crawford,  Nebraska. 

gravel,  sand,  or  clay  is  washed  from  the  lands  into  the 
ocean  and  deposited  on  the  ocean  floor;  the  finest  par- 
ticles being  carried  farthest  from  the  shore.  In  the  course 
of  ages  these  layers  of  sediment  are  changed  into  solid  rock 
(Figures  240-241).  Sandstone  and  limestone  are  classes 
of  sedimentary  rocks.  Sandstone  is  formed  by  particles 


SOILS 


283 


FIG.  242.  —  Limestone,  Logan  County, 
Ohio. 


of  sand  cemented  together, 
while  limestone  is  made 
from  the  remains  of  dead 
sea  animals  (Figure  242). 
Metamorphic  rocks  are 
modified  forms  of  either 
igneous  or  sedimentary 
rocks.  Heat  and  pressure 
are  the  agents  which  pro- 
duce these  changes  (Fig- 
ure 243). 

The  surface  of  the  earth  differs  from  place  to  place  due 
to  the  variety  of  positions  in  which  these  rocks  are  placed. 

In  some  regions  the 
surface  is  folded  into 
mountains,  in  other 
regions  there  are  deep 
basins  filled  with  the 
water  of  the  oceans. 

Weathering.  - 
The  changes  in  the 
earth's  surface  which 
are  due  to  atmos- 
pheric conditions  are 
called  weathering. 
Rocks  which  are  ex- 
posed  to  the  atmos- 
phere are  gradually 
decomposed.  The 
rate  of  the  decompo- 
sition depends  upon 
the  climate.  If  the 

FIG.  243.  —  Metamorphic  Rock.  .  . 

Granite  quarries,  Concord,  N.  H.  climate  IS  moist   and 


284 


GENERAL  SCIENCE 


is  subject  to  quick  changes  in  temperature,  the  weathering 
takes  place  much  more  rapidly  than  in  a  warm  and  dry 
climate  (Figure  244). 

Experiment  72.  —  Fill  a  small  bottle  with  water,  cork  tightly, 
and  place  in  a  freezing  mixture.  What  is  the  effect  upon  the 
bottle?  What  would  be  the  effect  if  water  in  the  pores  or  cracks 
of  a  rock  should  freeze  ? 

Some  rocks  weather  much  more  rapidly  than  others. 
It  is  interesting  to  note  the  changes  that  take  place  on 

the  tombstones  due  to 
weathering.  In  the  east- 
ern half  of  the  United 
States  many  of  the  in- 
scriptions are  illegible  on 
tombstones  that  have  been 
standing  for  50  or  60 
years. 

The  uneven  contraction 
and  expansion  of  rocks 
due  to  the  summer  heat 
sometimes  causes  them  to 
chip  and  crack.  The  roots  of  plants  penetrate  the  crevices 
of  rocks  and  split  them  apart,  as  they  grow  in  size.  Water 
at  times  may  acquire  acid  properties  in  passing  through 
decaying  vegetable  material,  which  makes  it  a  solvent  for 
some  of  the  materials  of  the  rock. 

How  Soil  Is  Made. — If  we  examine  the  soil  in  any  field, 
we  find  that  there  is  a  dark  layer  of  humus  on  top  (Figure 
245).  The  richness  of  the  soil  may  be  quite  accurately 
estimated  from  the  depth  of  this  layer  of  dark  earth. 
The  deeper  the  layer  of  dark  earth  the  richer  the  soil. 
The  dark  color  of  this  layer  is  caused  by  the  decayed  plants 
it  contains.  Plants  turn  black  as  they  rot.  As  we  go 


FIG.  244.  —  Exposed  Shales,  Showing 
Effects  of  Weathering. 


SOILS 


285 


Showing  Soil  Above  the  Shale,  then 
Solid  Rock  Below. 


downward  the  color  gradually  changes  to  a  lighter  brown, 
and  still  deeper  the  stain  of  the  decaying  plants  is  no 
longer  seen ;  the  soil  becomes  harder  and  harder  until  we 
finally  reach  the 
solid  rock. 

This  is  the  com- 
mon sort  of  soil 
found  all  over  the 
world.  It  is  made 
by  the  gradual  de- 
cay of  the  rock 
(Figure  246).  If 
we  should  remove 
all  the  soil  from 
an  area  of  rock,  it 
would  immediately 
begin  to  form  again.  After  a  few  years'  exposure  to 
the  atmosphere,  the  rock  would  be  decayed  enough  so 
that  lichens  and  certain  mosses  would  find  a  place  to 
grow.  They  would  aid  in  keeping  the  surface  of  the 
rock  moist  and  thus  aid  weathering.  The  decay  of 
these  simple  plants  would  produce  a  little  humus,  and 
soon  the  seeds  of  other  larger  plants  would  germinate 
and  grow  there.  The  decay  of  these  plants  gradually 
adds  to  the  layer  of  mold  on  the  surface  of  the  rock 
until  the  largest  trees  may  find  a  place  to  grow.  The 
atmosphere,  the  water,  the  decay  of  plants,  the  roots 
of  the  plants,  and  other  minor  agencies  are  all  at  work 
now  deepening  and  enriching  the  soil.  Of  course  this 
change  may  take  centuries,  but  when  compared  with 
the  enormous  age  of  the  earth  it  seems  a  very  short 
time. 

Glaciated  Soil.  —  In  the  northern  portions  of  our  conti- 


286  GENERAL  SCIENCE 

nent  the  glaciers  of  the  ice  age  had  considerable  to  do  with 
the  soils  of  certain  sections.  As  these  great  fields  of 
ice  moved  south  they  carried  great  quantities  of  material 
from  the  old  mountain  chains  of  Southern  Canada. 
This  rich  material  was  distributed  over  the  northern 


FIG.  246.  —  Mountain  Disintegration  in  the  Alps. 
The  accumulated  debris  on  the  right  is  rock  in  process  of  decay. 

part  of  the  United  States  to  be  ground  finer  and  redis- 
tributed with  each  return  of  the  glacier  (Figure  247). 
Many  regions  owe  the  fertility  of  their  soils  largely  to  the 
work  done  by  the  great  seas  of  ice. 

Composition  of  Soils.  -  -  The  wealth  of  our  agricultural 
communities  lies  in  the  fertility  of  their  soils.  An  agri- 
cultural soil  is  made  of  (a)  decayed  rock,  (6)  soil  water, 
(c)  soil  air,  (d)  decaying  organic  matter,  (e)  living  organ- 
isms. In  general  we  may  say  that  fertile  soils  have  all 
of  the  above  constituents  ;  however,  drained  swamp  lands 
(muck  soils)  are  usually  very  fertile  although  deficient 
in  rock  particles. 


SOILS 


287 


The  richness  of  the  soil  will  first  depend  upon  the  com- 
position of  the  underlying  rock  and  next  upon  the  action 
of  the  plants  which  yield  the  organic  matter. 


U.  S.  Geological  Survey. 
FIG.  247.  —  Erratic  Bowlders. 

These  bowlders  have  been  deposited  by  the  glacial  stream. 

In  most  soils  the  rock  particles  predominate,  making  up 
from  60  per  cent  to  95  per  cent  of  the  total  weight.  From 
two  to  five  per  cent 
is  organic  matter, 
and  most  of  the  re- 
mainder is  water. 

Experiment  73.  - 

Shake  a  quantity  of 
soil  with  water  in  a 
bottle  (Figure  248), 
until  all  the  particles 
of  the  soil  are  broken  FIG.  248. 


medium 
sand 


288 


GENERAL  SCIENCE 


up  and  in  a  state  of  suspension  in  the  water.  Allow  the  mixture  to 
settle  for  five  minutes  and  then  pour  the  roily  water  into  another 
bottle,  leaving  the  particles  which  have  already  settled  in  the  first 
bottle.  After  five  more  minutes  again  pour  off  the  roily  water.  Do 
this  five  times,  leaving  the  water  in  the  last  bottle  until  all  the 
particles  have  settled,  when  the  clear  water  may  be  poured  off. 


medium          fine 
sand  sand 

4.5  %  40  % 

FIG.  ,249. 


Compare  the  size  of  the  particles  in  the  different  bottles.  As  many 
divisions  as  desired  may  be  made  in  this  way.  Figure  249  shows 
the  composition  of  sandy  loam,  which  is  an  excellent  soil. 

Table  Showing  Mechanical  Analysis  of  Soils.  - 


>  '  f 

DIAMETER  OF 
PARTICLES 

NORFOLK 
SAND 

MIAMI  SILT 
LOAM 

WAS  ASH 
CLAY 

Fine  gravel      .... 
Coarse  sand    .     .     .     . 
Medium  sand       .     .     » 
Fine  sand        . 

2-1  mm. 
1-0.5  mm. 
0.5-0.25  mm. 
0.25-0.10  mm. 

.3 
.15 
.22 

.38 

.0 

.1 
.1 

.2 

.0 

.1 
.1 

.3 

Very  fine  sand     .     . 
Silt                        .     .     . 

0.10-0.05  mm. 
0.05-0.005  mm. 

.10 

.8 

.8 
.73 

.7 
.49 

Clav 

0.005-0  mm. 

.4 

.15 

.37 

Names  of  Soils.  —  Clay  soils  are  those  which  contain  a 
large  proportion  of  the  smallest  particles,  while  those  that 
contain  a  large  proportion  of  sand  are  simply  called 
sandy  soils  or  sands.  Loams  are  intermediate  mixtures 
of  sand  and  fine  particles. 


SOILS 


289 


Norfolk  sand  is  one  of  the  common  soils  of  the  Atlantic 
flood  plain.  Miami  silt  loam  is  found  in  the  corn  belt  of 
the  central  west.  Wabash  clay  occurs  along  most  of  the 
river  bottoms  of  the  Mississippi  valley. 

Experiment  74.  —  Arrange  several  lamp  chimneys  as  shown  in 
Figure  250  each  containing  a  different  kind  of  soil.  Pour  water  in 
the  pan,  and  after 
allowing  it  to  stand 
for  an  hour  note  the 
height  of  the  water  in 
each  chimney.  The 
capillary  action  of 
each  soil  may  be  de- 
termined in  this  way. 

Importance  of 
Size  of  Soil  Parti- 
cles. — The  water- 
holding  power  of 
soils  depends 
largely  upon  the 
surface  area  of  the  particles  composing  the  soil.  The 
finer  the  particles  the  greater  will  be  the  amount  of 
water  that  this  kind  of  soil  will  hold.  The  finest  soil 
particles  are  less  than  one-thousandth  of  a  millimeter  in 
diameter.  The  total  surface  area  of  a  cubic  foot  of  such  a 
soil  would  be  enormous.  Such  soils  have  a  high  water 
capacity ;  that  is,  they  will  still  hold  a  large  amount  of 
water  after  the  free  water  has  been  allowed  to  drain  outt 
Clay  soils  have  the  highest  water  capacity,  sometimes  as 
high  as  forty  per  cent ;  and  sandy  soils  have  the  lowest 
water  capacity.  In  addition  to  influencing  the  water 
capacity  of  soils,  the  size  of  the  particles  also  affects  the 
movements  of  the  soil  air,  the  amount  of  food  that  can  be 


FIG.  250. 


290 


•  GENERAL  SCIENCE 


dissolved  for  plant  use,  the  growth  of  soil  organisms,  and 
the  temperature  of  the  soil. 

Experiment  75.  —  Close  the  bottom  of  a  tall,  straight  lamp 
chimney  and  fill  it  with  soil,  then  pour  it  full  of  water.  If  a  hole 
is  now  made  in  the  stopper  (Figure  251),  a  considerable  portion  of 
the  water  will  drain  out.  This  is  called  gravitational  water.  Why  ? 
If  the  hole  at  the  bottom  is  again  closed  and  the  apparatus  is 

allowed  to  stand  for  some  time,  the 
soil  will  become  quite  dry,  since  the 
water  in  the  bottom  will  rise  by  the 
action  of  capillarity  to  replace  that 
lost  at  the  surface  by  evaporation. 
The  water  lost  in  this  way  is  called 
capillary  water.  If  some  of  this  dry 
soil  is  weighed  and  then  heated  to  a 
temperature  of  100°  C.,  it  will  lose  still 
more  water.  This  is  called  hygroscopic 
water  and  is  so  strongly  held  in  the  soil 
that  it  is  not  available  for  plant  use. 

Size  of  Soil  Particles  in  Rela- 
tion to  Temperature  and  Crops. 
-  We  have  learned  that  evapora- 
tion of  water  lowers  the  tempera- 
ture of  the  surrounding  objects ; 
therefore  that  soil  will  be  coldest 
from  which  the  most  water 
evaporates.  Wet  soils  are  always  cold  soils.  Clay  soils 
are  colder  than  sandy  soils  for  this  reason.  They  have 
a  larger  water  capacity  and  hence  furnish  more  water  for 
evaporation.  An  additional  reason  for  the  coldness  of 
wet  soils  is  that  the  heat  capacity  of  dry  soil  is  but  two 
tenths  that  of  water ;  that  is,  it  takes  five  times  as  much 
heat  to  warm  a  gram  of  water  through  one  degree  as  it 
does  to  warm  a  gram  of  dry  soil  through  one  degree. 
Hence  the  sun's  heat  will  warm  the  drier  soil  more  rapidly. 


FIG.  251. 


SOILS  291 

Plant  food  must  be  in  the  form  of  solutions.  Since  the 
water  touches  more  surface  in  a  given  volume  of  soil  when 
the  particles  are  small  than  when  they  are  large,  it  will 
be  able  to  dissolve  and  furnish  plant  food  more  readily  in 
the  finer  soils.  On  thepther  hand,  the  coarser  soils  will  be 
better  aerated,  due  to  the  fact  that  the  spaces  between  the 
particles  are  larger  so  that  the  air  moves  more  freely. 

All  of  these  things  affect  the  crops  that  grow  in  the  soils. 
Sandy  soils  which  are  well  adapted  for  corn,  potatoes,  and 
market  gardening  are  not  well  adapted  for  wheat,  which 
may  be  grown  to  advantage  on  the  heavier  clay  soil.  The 
successful  farmer  will  soon  learn  what  crops  are  suited 
to  his  land  and  cease  cultivating  those  that  are  not. 

Conservation  of  the  Soil.  -  -  The  study  of  the  soil  and 
its  products  will  soon  convince  us  that  it  is  quite  important 
to  care  properly  for  this  great  gift  to  man.  It  has  required 
ages  for  the  soils  to  be  formed  and  reach  a  certain  produc- 
tive stage,  but  it  requires  but  a  few  years  of  careless  farm- 
ing to  reduce  them  to  a  non-paying  productive  basis. 
The  population  of  the  United  States  is  increasing  rapidly, 
and  this  means  that  the  demands  on  the  soil  are  increasing 
proportionately.  It  is  not  possible  to  harvest  crops  year 
after  year  and  put  nothing  back  on  the  land  without 
decreasing  its  fertility.  Certain  crops  take  certain  kinds 
of  food  from  the  soil  with  the  inevitable  result  that  the 
amount  of  this  particular  food  in  the  soil  is  lessened. 

Measure  of  Soil  Values.  —  A  soil  from  the  agricultural 
standpoint  is  measured  by  the  abundance  of  its  scarcest 
element.  There  are  five  substances  in  which  our  soils 
are  likely  to  be  deficient :  water,  nitrogen,  phosphoric  acid, 
potash,  and  lime.  These  foods  are  needed  by  different 
crops  in  varying  quantities.  If  the  soil  is  deficient  in 
phosphoric  acid,  the  addition  of  phosphoric  acid  will 


292  GENERAL  SCIENCE 

increase  the  crop.  Suppose  that  the  average  crop  of  corn 
in  a  certain  kind  of  soil  is  80  bushels  to  the  acre,  but  that 
the  supply  of  nitrogen  is  so  small  as  to  limit  the  crop  to  60 
bushels  to  the  acre,  and  that  the  supply  of  potash  limits 
the  crop  to  50  bushels  to  the  acre.  Then  of  course  the 
crop  will  be  50  bushels,  if  there  are  no  other  deficiencies. 
In  such  a  case  the  problem  is  to  determine  what  the  soil 
lacks  and  then  add  these  materials. 

A  soil  may  decrease  in  productivity  from  a  number  of 
causes. 

1.  It  may  lose  its  power  to  hold  water.     This  may  be 
remedied  by  tile  drainage  and  the  addition  of  humus. 

2.  The  supply  of  available  plant  food  may  be  exhausted 
by  raising  the  same  crops  year  after  year.     This  may  be 
remedied  by  the  addition  of  fertilizers  and  by  drainage. 

3.  The  soil  may  become  acid  and  unfavorable  for  the 
growth  of  soil  organisms.     In  such  cases  an  application  of 
lime  is  beneficial. 

The  fertility  of  soils  depends  largely  on  the  humus  they 
contain.  Humus  is  simply  decayed  organic  matter. 
Humus  in  soil  increases  its  capacity  for  holding  water, 
furnishes  nitrogen  by  its  decomposition,  and  gives  an 
acidity  to  water  which  makes  it  a  better  solvent  for  other 
plant  foods.  The  farmer  should  never  lose  an  opportunity 
to  add  humus  to  his  soil,  since  it  not  only  contains  plant 
food  elements  but  renders  available  much  of  the  food 
that  is  already  in  the  soil.  Decayed  vegetable  matter  and 
manures  are  excellent  sources  of  humus. 

Fertilizers.  —  It  is  quite  a  common  idea  that  soils  may 
be  analyzed  to  determine  what  fertilizers  should  be  used 
on  them.  In  general  this  is  true  ;  however,  the  chemical 
analysis  only  shows  the  amounts  of  different  substances 
present  and  not  the  amounts  of  available  foods.  Experi- 


SOILS  293 

ment  is  the  most  reliable  way  of  determining  what 
additions  should  be  made  to  the  land  in  the  form  of  fer- 
tilizers. 

Barnyard  manure  and  growing  plants  plowed  under 
are  the  best  kinds  of  fertilizers  (Figure  252). 


FIG.  252.  —  Results  Obtained  from  Using  Different  Fertilizers. 
Barnyard  manure  Unfertilized 

History  tells  us  that  the  Indians  used  a  fish  in  each 
hill  of  corn  to  fertilize  it. 

Commercial  fertilizers  usually  contain  nitrogen,  potash, 
and  phosphoric  acid.  Lime  in  its  ordinary  form  is  also 
used. 

Nitrogen  as  a  Fertilizer.  —  Nitrogen  is  a  necessary  plant 
food.  It  may  be  applied  to  the  soil  as  barnyard  manure, 
sodium  nitrate,  ammonium  sulphate,  potassium  nitrate, 
slaughter-house  refuse,  cotton-seed  and  linseed-oil  meal, 
and  other  forms  of  plant  refuse.  The  most  common  form 
in  which  nitrogen  is  sold  as  a  commercial  fertilizer  is  Chile 
saltpeter  or  sodium  nitrate.  It  contains  about  16  per 
cent  of  nitrogen. 


294 


GENERAL  SCIENCE 


Ammonium  sulphate,  a  by-product  of  the  manufacture 
of  coke,  contains  about  20  per  cent  of  nitrogen. 

Dried  blood,  tankage,  and  bone  meal  are  all  good  ferti- 
lizers and  contain  considerable  nitrogen  which  is  rendered 
available  by  the  action  of  soil  bacteria.  This  fact  makes 
it  slower  in  its  action  and  more  desirable  for  many  crops 
than  sodium  nitrate,  which  is  •  very  soluble  and  therefore 
likely  to  leach  out  of  the  soil. 

Potassium  as  a  Fertilizer.  —  Wood  ashes  contain  much 
potash  and  would  make  an  excellent  fertilizer  if  the 


FIG.  253.  —  Results  Obtained  from  Using  Different  Fertilizers. 

Unfertilized  Nitrogen 

Phosphorus 
Potassium 


supply  were  not  so  limited.  The  common  commercial 
forms  of  potash  are  muriate  of  potash  and  sulphate  of 
potash  (Figure  253). 

Nearly  all  of  the  potash  used  in  America  was  formerly 
manufactured  from  Kainit  from  the  mines  of  Germany  in 
the  form  of  muriate  or  sulphate  of  potash. 


SOILS 


295 


Phosphorus  as  a  Fertilizer.  —  Fertilizers  containing 
phosphorus  are  barnyard  manure,  phosphate  rock,  packing 
house  wastes,  and  basic  slag  (Figure  254). 

The  phosphate  rock,  found  in  many  parts  of  the  United 
States,  particularly  in  South  Carolina,  Tennessee,  and 
Florida,  furnishes  most  of  the  phosphorus  used  in  fertilizers. 


FIG.  254.  —  Results  Obtained  from  Using  Different  Fertilizers. 

Nitrogen  Unfertilized 

Phosphorus 

Lime  as  a  Fertilizer.  —  While  lime  is  not  exactly  a 
positive  plant  food,  it  renders  a  valuable  service  to  plants. 
It  is  used  to  correct  soils  that  have  become  acid,  and  it 
assists  in  the  liberation  of  other  plant  foods  (Figure  255). 

How  to  Experiment  with  Fertilizer.  —  The  kind  of  fer- 
tilizer that  is  best  suited  for  a  particular  soil  may  be  deter- 
mined easily  by  experiment.  A  small  plot  of  land  should 
be  divided  into  several  equal  areas,  or  boxes  may  be  used 
as  shown  in  Figure  256 ;  in  one  box  sodium  nitrate  may 
be  used,  in  another  phosphate  rock,  in  another  potassium 
nitrate,  in  another  lime,  and  in  still  other  boxes  combina- 


296  GENERAL  SCIENCE 

tions  of  different  fertilizers  may  be  used.  The  yields  in  the 
different  boxes  will  give  a  definite  measure  of  the  relative 
value  of  the  different  fertilizing  materials  on  the  soil  tested. 


FIG.  255.  —  Showing  the  Value  of  Lime  on  Sour  Soil. 

The  experiment  station  bulletins  of  the  different  states 
usually  give  quite  accurate  information  concerning  soil 
fertility  and  the  materials  needed  in  fertilizers.  "  On 
practically  all  Ohio  soils  that  have  been  for  any  length 
of  time  in  cultivation,  possibly  excepting  mucks,  phos- 
phorus must  be  supplied  before  the  maximum  yield  of  any 
crop  can  be  attained.  The  longer  the  land  has  been  in 
cultivation,  the  greater  the  need  of  phosphorus."  l 

Why  we  Cultivate.  —  There  are  a  number  of  reasons  for 
cultivating  the  soil  while  crops  are  being  grown.  Culti- 
vation destroys  weeds  which  would  otherwise  take  the 
1  Ohio  Circular  No.  79. 


SOILS 


297 


FIG.  256. 

plant  food  which  the  crop  needs.  It  conserves  the  soil 
moisture  by  putting  the  soil  in  a  condition  to  absorb  the 
rainfall  and  also  by  preventing  evaporation  by  forming  a 
layer  of  dust  mulch  on  the  surface  and  by  breaking  up 
capillary  connections. 

Since  in  most  parts  of  the  United  States  the  rainfall  is 
insufficient  during  the  growing  months  for  the  production 
of  maximum  crops,  it  is  quite  essential  that  the  ground  be 
cultivated  as  soon  as  possible  after  rains.  The  first  effect  of 
cultivation  is  to  increase  evaporation,  but  soon  the  loose 
dry  soil  on  the  surface  acts  as  a  mulch  to  retard  evaporation. 

Dry  Farming.  —  A  large  part  of  the  United  States  has 
insufficient  rainfall  to  raise  good  crops  without  irrigation. 
In  some  of  the  western  states  it  has  been  possible  to  conserve 
the  greater  part  of  the  rainfall  for  one  or  more  years  for 
the  use  of  crops  during  the  growing  season.  This  is  called 
dry  farming  and  is  accomplished  by  first  plowing  the 
ground  to  a  depth  of  eight  or  ten  inches  and  then  cultivat- 
ing continuously,  so  that  a  dry  dust  mulch  is  formed  on 
the  top  of  the  ground.  The  water  that  falls  as  rain  is 
quickly  absorbed  and  held  as  capillary  water  by  the  soil. 
Capillary  water  moves  very  slowly  through  the  dry  dust 
mulch,  and  thus  the  loss  by  evaporation  is  reduced  to  a 
minimum.  When  sufficient  water  has  collected  in  the  soil, 


298  GENERAL  SCIENCE 

a  crop  is  grown.     A  crop  is  usually  grown  every  other 
year ;  but  sometimes  two  crops  are  grown  in  three  years. 

Experiment  76.  —  To  determine  the  per  cent  of  water,  organic 
matter,  and  mineral  matter  in  soils.  Weigh  a  crucible.  Place  ten 
grams  of  the  soil  to  be  tested  in  it.  Heat  to  a  temperature  of  110° 
Centigrade  and  maintain  this  temperature  for  an  hour.  Weigh 
again.  The  loss  shows  how  much  water  was  evaporated.  Now 
heat  the  remainder  to  a  red  heat  and  maintain  for  an  hour.  The 
loss  this  time  shows  the  amount  of  organic  matter  in  this  soil,  and 
the  residue  shows  the  amount  of  mineral  matter.  Figure  the  dif- 
ferent values  in  per  cents.  Test  a  number  of  soils  in  this  way. 
What  kind  of  soils  contain  the  most  water?  v  The  most  organic 
matter  ? 

QUESTIONS 

1.  Explain  how  an  exchange   of  products  benefits   both  the 
farmer  and  the  manufacturer. 

2.  Do  field  stones  become  larger  or  smaller?     Why? 

3.  What  kind  of  rock  is  slate?     Marble?     Sandstone?     How 
is  each  kind  formed? 

4.  WThat  is  the  relative  surface  area  of  a  one-foot  cube  of  stone 
and  the  same  stone  divided  into  one-half  inch  cubes  ? 

5.  What  climates  facilitate  weathering? 

6.  Where  are  the  humus  colored  soils  thickest,  on  the  hills  or 
in  the  valleys?     Why? 

7.  Why  are  some  soils  red?     Blue? 

8.  Are  there  glacial  boulders  in  your  country?     From  where 
did  they  come?     Are  there  any  evidences  that  glaciers  once  covered 
the  region? 

9.  What  are  the  necessary  elements  in  an  agricultural  soil? 

10.  What  kind  of  soil  predominates  in  your  region? 

11.  What  is  the  value  of  air  in  the  soil? 

12.  Why  are  sandy  soils  warmer  than  clay  soils? 

13.  What  is  the  advantage  in  mixing  your  own  commercial 
fertilizers  over  buying  them  already  mixed? 

14.  What  determines  the  water  capacity  of  soils? 

15.  What  crops  in  your  region  require  the  least  rain?     Name 
some  wet  season  crops. 

16.  Should  corn  cultivation  be  deep?     Why? 


CHAPTER   XVIII 
SURFACE   WATER,  DRAINAGE,  AND  IRRIGATION 

What  Becomes  of  the  Rainfall. — When  water  falls  upon 
the  earth  as  rain,  it  may  do  any  one  of  three  things.  It 
may  evaporate  and  return  to  the  air ;  it  may  run  off 
in  little  streams  to  join  other  streams  and  finally  reach  the 
ocean ;  it  may  sink  into  the  ground  and  reach  under- 
ground streams  or  remain  in  the  soil  as  capillary  water. 

How  the  rainfall  is  disposed  of  depends  upon  the  nature 
of  the  earth  upon  which  it  falls  and  also  upon  the  intensity 
of  the  rainfall.  If  the  rain  falls  gently  upon  loose  soil  or 
upon 'soil  that  is  covered  with  vegetation,  most  of  it  will 
sink  into  the  earth ;  but  if  it  falls  rapidly  upon  a  hard, 
sloping  surface,  most  of  the  water  will  run  off  as  surface 
water.  Many  of  us  have  noticed  the  little  streams  that 
so  quickly  assume  torrential  proportions  after  a  very  hard 
rain. 

Ground  Water.  —  Under  the  influence  of  gravity  the 
free  water  that  sinks  into  the  soil  percolates  downward 
until  it  reaches  an  impervious  layer  of  rock.  It  now  flows 
over  the  top  of  that  layer  in  the  direction  of  its  inclination 
until  it  finds  an  outlet  as  a  spring  or  line  of  seepage  on  the 
side  of  a  hill  or  valley.  If  rock  layers  occur  in  alter- 
nately porous  and  impervious  strata  and  dip  toward 
a  fault  fissure  which  appears  at  the  surface  at  a  lower 
level  than  the  outcrop  of  the  rock  layers,  water  will 
be  forced  out  of  the  fissure.  This  is  the  same  principle 

299 


300  GENERAL  SCIENCE 

as  that  involved  in  the  artesian  well,  in  which  a  bored 
hole  takes  the  place  of  the  fissure  crack. 

Caves  and  caverns  are  often  formed  by  the  dissolving 
of  the  mantle  rock,  such  as  limestone,  by  the  ground 
water.  The  Mammoth  Cave  in  Kentucky,  Luray  Cavern 
in  Virginia,  and  Wyandotte  Cave  in  Indiana  are  good 
examples  of  this  action  of  ground  water  (Figure  257). 

Work  of  Ground  Water.  --  The  greatest  work  done  by 
ground  water  is  due  to  its  power  of  dissolving  other  sub- 
stances. Some  of  these  substances  water  dissolves  easily, , 
while  others  are  dissolved  only  after  the  water  has  become 
charged  with  carbon  dioxide  as  it  does  in  passing  through 
decaying  vegetation.  If  it  were  not  for  this  power  that 
water  has  of  dissolving  all  substances,  life  would  be 
impossible.  Plants  and  animals  are  dependent  upon  their 
circulations,  which  are  simply  currents  of  water  in  the  form 
of  sap  or  blood,  carrying  food  in  solution  to  the  different 
parts  of  their  being.  The  foods  that  plants  take  from  the 
soil  must  first  be  dissolved.  The  same  is  true  of  the  food 
of  animals ;  it  must  be  dissolved  before  it  can  be  used  by 
the  body. 

Water  is  also  a  great  distributing  agent.  It  distributes 
food  to  plants  and  animals  on  land  and  sea.  It  aids  in  the 
distribution  of  heat  through  the  agency  of  ocean  currents, 
and  it  distributes  material  for  the  building  of  sedimentary 
rocks  on  the  ocean  floor. 

River  Formation.  --  The  water  that  falls  as  rain  and  is 
neither  evaporated  nor  absorbed  by  the  soil  collects  in 
little  streams  and  runs  off  toward  the  sea.  Along  its 
course  it  is  joined  by  other  surface  streams  and  also  by 
underground  streams  and  the  water  from  springs  until  it 
is  large  enough  to  be  called  a  river.  A  river  is  simply  a 
large  stream  of  water  which  is  bearing  the  run-off  water 


FIG.  257.  —  The  Work  of  Underground  Waters. 

The  Hermannshohle,  in  the  Harz  Mountains,  Germany,  showing  stalactites 
and  stalagmites.  These  are  deposits  of  calcium  carbonate,  formed  by  the 
waters  which  have  passed  through  and  partially  dissolved  the  overlying 
limestone. 

301 


302 


GENERAL  SCIENCE 


and  the  waste  of  the  land  from  higher  to  lower  ground. 
Usually  rivers  flow  to  the  sea.  The  principal  stream  and 
all  the  branches  that  flow  into  it  constitute  a  river  system 
(Figure  258).  The  term  "  river  "  is  usually  applied  to  the 
main  stream  or  tb  the  larger  branches  of  a  river  system, 


FIG.  258.  —  The  Mississippi  River  System. 

while  the  term  "  stream  "  is  a  general  term  and  is  used 
quite  indiscriminately  and  with  little  reference  to  size. 

Lakes  and  Inland  Seas.  —  A  great  deal  of  the  surface 
water  in  some  regions  drains  into,  depressions.  When  a 
depression  is  filled,  the  water  runs  over  the  lowest  part 
of  its  rim  and  continues  its  course  to  the  sea.  If  these 
bodies  of  water  are  small,  we  call  them  ponds  ;  if  they  are 
large,  we  call  them  lakes.  Lakes  are  constantly  being 
filled  by  the  land  waste  that  is  carried  by  the  inflowing 
rivers.  If  the  lake  has  an  outlet,  the  water  in  it  is  usually 
very  clear,  due  to  the  fact  that  all  the  sediment  has  been 
deposited  on  the  bottom.  The  outlet  of  the  lake  slowly 


SURFACE  WATER,  DRAINAGE,  AND  IRRIGATION     303 

wears  away  its  bed  and  thus  lowers  the  level  of  the  water 
behind  it.  Lakes  may  J)e  considered  as  enlargements  in 
a  river's  course.  The  river  is  constantly  at  work  to  remove 
this  enlargement  both  by  filling  and  by  draining  the  lake. 
There  are  no  lakes  in  an  old  river  system  for  this  reason. 
Lakes  are  quite  useful  to  civilized  man.  They  often 
form  valuable  inland  waterways,  as  in  the  case  of  the 


FIG.  259.  —  Flood,  Dayton,  Ohio  (March,  1913). 

Great  Lakes  of  North  America,  the  Caspian  Sea,  or  the 
Lakes  of  Africa.  Being  quite  large  they  act  as  reservoirs 
for  excess  water.  There  are  no  floods  in  the  St.  Lawrence 
River  system,  while  in  the  Mississippi  valley  there  are 
destructive  floods  almost  every  year  (Figure  259). 

When  the  rainfall  of  a  region  is  insufficient  to  furnish 
enough  water  to  fill  depressions  to  overflowing,  salt 
lakes  occur.  The  streams  which  flow  into  the  depression 


304  GENERAL  SCIENCE 

carry  sediment  and  also  various  salts  in  solution.  The 
evaporation  of  the  water  from  the  surface  of  the  lake 
increases  the  density  of  these  solutions.  Great  Salt  Lake 
has  about  15  per  cent  of  various  salts  in  solution,  and  the 
Dead  Sea  has  even  more. 

Work  of  Rivers.  —  All  streams  carry  sediment  down 
their  valleys.  In  flood  times  the  amount  of  sediment  is 
large  enough  to  make  the  water  muddy  in  quite  small 
streams,  while  in  many  of  the  largest  rivers  the  water 
is  always  muddy.  Besides  carrying  sediment  in  suspen- 
sion, streams  roll  sand,  gravel,  and  even  large  stones  along 
their  beds.  Much  of  this  coarse  material  picked  up  in 
flood  time  by  a  stream  is  carried  for  a  distance  and  dropped 
as  the  current  of  the  stream  becomes  slower.  This  coarse 
material  will  be  picked  up  again  when  the  next  high  water 
occurs.  A  large  part  of  the  suspended  sediment  in  such 
rivers  as  the  Mississippi  River  is  carried  to  the  ocean  and 
dropped  near  the  shore.  It  is  estimated  that  the  Missis- 
sippi River  carries  an  average  of  more  than  a  million  tons 
of  suspended  material  into  the  Gulf  of  Mexico  every  day. 
In  addition  to  this  it  carries  a  great  deal  of  material  in 
solution. 

All  the  rivers  of  the  world  are  constantly  at  work  carry- 
ing materials  from  the  land  to  the.  sea.  The  sediment 
carried  by  a  stream,  including  that  rolled  along  its  bed,  is 
called  its  load. 

Erosion.  —  The  wearing  away  of  the  materials  which 
form  the  earth's  crust  is  called  erosion.  It  is  due  mainly 
to  the  mechanical  action  and  the  dissolving  power  of  the 
surface  water.  Even  the  hardest  rocks  are  decomposed 
by  these  agencies.  In  regions  which  are  sufficiently  cold 
the  action  of  the  frost  also  aids  in  wearing  away  the 
surface  rock. 


SURFACE  WATER,  DRAINAGE,  AND  IRRIGATION     305 

As  the  softer  portions  of  the  rocks  are  dissolved  by  the 
water,  they  break  apart  ,1m til  the  pieces  are  small  enough 
to  be  moved  by  the  running  water.  The  larger  pieces  are 
usually  started  in  time  of  high  water,  since  the  carrying 
power  of  running  water  increases  enormously  as  the  veloc- 
ity is  increased.  As  the  loose  material  is  rolled  along,  the 


FIG.  260.  —  An  Example  of  Water  Erosion. 

solid  surfaces  in  the  bed  of  the  stream  are  cut  down  and 
the  material  produced  is  moved  away  by  the  force  of  the 
current.  This  work  is  called  water  erosion. 

Erosion  is  taking  place  over  nearly  all  of  the  exposed 
surface  of  the  earth.  When  there  is  a  heavy  rain,  many 
miniature  streams  are  formed  on  the  surface  of  the  earth. 
These  little  streams  all  do  their  share  in  erosion,  each  one 
carrying  away  a  small  part  of  the  surface  material  and  each 


306 


GENERAL  SCIENCE 


leaving  its  little  path  for  another  similar  stream  when  the 
next  rain  occurs.     (Figures  260,  261.) 

When  the  surface  water  is  concentrated  into  a  perma- 
nent stream,  the  work  of  eroding  its  bed  goes  on  rapidly. 
Each  flood  period  makes  many  changes  in  the  stream  bed. 
Some  streams  have  cut  deep  gullies  or  troughs  for  them- 


U.  S.  Geological  Survey. 

FIG.  261.  —  Bad  Lands,  Scott's  Bluff,  Nebraska,  Showing  Gullies  Made  by 
Water  Erosion. 


selves.  The  run-off  water  sometimes  scars  the  slopes 
of  hillside  farms  in  this  way,  but  usually  such  gullies  are 
an  indication  of  careless  farming.  The  rapidity  of  the 
cutting  by  a  stream  depends  upon  the  material  of  the 
stream  bed,  the  fall  of  the  stream,  and  the  quantity  of 
water. 

The  irregular  erosion  of  stream  beds  produces  the  char- 
acteristic features  of  streams  known  as  falls,  rapids,  and 


SURFACE  WATER,  DRAINAGE,  AND  IRRIGATION     307 


reaches  (Figure  262) . 
However,  streams  are 
always  at  work  to 
remove  such  features 
after  they  are  made 
and  to  reduce  their 
beds  to  an  even  grade. 
Thus  old  rivers  are 
devoid  of  rapids  and 
falls. 

-.''"..  FIG.  262.  — Niagara  Falls. 

In  climates  of  mod- 
erate or  heavy  rainfall,  the  erosion  of.  the  land  is  usually 
rapid  enough  to  produce  wide  valleys ;   but  in  regions 
of   scant    rainfall,    the    streams    cut    their    beds    much 

faster  than  the 
adjacent  land  is 
eroded,  and  deep 
gullies  or  canons 
result. 

The  Colorado  is 
the  best  example 
of  such  a  river 
(Figure  263).  It 
flows  hundreds 
of  miles  through 
canons  varying  in 
depth  from  a  few 
hundred  feet  to 
several  thousand 
feet.  The  veloc- 
ity of  this  river 
is  so  great  that 

U.  S.  Geological  Survey. 
FIG.  263.  —  Grand  Canon,  Arizona.  the        Sand       and 


308 


GENERAL  SCIENCE 


gravel  it  carries  is  rapidly  deepening  its  channel,  while 
the  lofty  sides  of  its  canon  are  little  changed  by  ages  of 
weathering. 

The  St.  Lawrence  River  carries  practically  no  sediment 
of  any  sort  and  so  erodes  its  course  very  slowly. 

Deposition.  —  Deposition,  like  erosion,  depends  very 
largely  upon  the  slope  of  the  river  bed  and  the  velocity  of 


FIG.  264.  —  The  Delaware  River  above  Water  Gap,  Pa. 

The  deposition  of  materials  in   the  bed  of  the  river  will  extend  to  form 

broad,  open  plains. 

the  current.  The  materials  carried  or  rolled  along  by 
rivers  are  deposited  at  various  points  in  their  channels  or 
carried  to  the  sea  (Figure  264).  The  finer  portions  of 
silt  may  reach  the  ocean,  where  it  is  deposited  over  the 
ocean  floor  or  in  huge  delta  bars  at  the  mouth  of  the  river, 
as  in  the  case  of  the  Mississippi  River  or  the  Nile  River 
(Figures  265,  266).  The  fine  sand  is  deposited  along  the 
lower  portion  of  a  river's  course.  As  we  go  up  the  river 
the  deposit  becomes  coarser,  until  in  the  upper  part  of  its 
course  we  find  stones  of  considerable  size. 


SURFACE  WATER,  DRAINAGE,  AND  IRRIGATION     309 


FIG.  265.  —  The  Mississippi  River  Delta. 


As  the  current  of  a  river  decreases  in  velocity,  its  carry- 
ing power  is  greatly  lessened,  and  some  of  its  load  must  be 
deposited.  The  Mississippi  River  flows  very  slowly  in 
the  lower  part  of  its  course 
and  as  a  result  has  been 
filling  up  its  channel. 
There  are  many  bars  in 
the  lower  Mississippi  which 
interfere  with  navigation. 
Boats  require  an  experi- 
enced pilot  because  of 
these  shifting  bars.  As 
the  bed  of  a  river  has 
been  raised  it  has  been  necessary  to  build  high  artificial 
banks  (levees)  to  keep  the  water  from  overflowing  the 
agricultural  land  and  doing  great  damage.  The  Govern- 
ment of  the  United 
States  annually 
spends  millions  of 
dollars  on  these 
levees. 

The  sediment 
left  by  streams  on 
the  land  in  times  of 
overflow  is  called 
alluvial  deposit. 
The  more  the  cur- 
rent is  checked,  the 
greater  will  be  the 
deposit.  In  some 
places  where  the  current  is  not  checked  the  swiftly  moving 
water  may  take  up  soil  instead  of  depositing  it.  Where 
silt  is  deposited,  the  land  will  be  enriched ;  while  of  course 


FIG.  266.  —  A  River  Delta. 


310  GENERAL  SCIENCE 

where  surface  earth  is  removed  by  running  water,  the  soil 
will  be  impoverished. 

Soil  Water.  -  -  The  productiveness  of  soil  is  limited  by 
the  amount  of  plant  food  that  it  contains.  Water  is  the 
most  important  plant  food.  Since  plants  are  able  to  take 
their  food  only  in  water  solutions,  the  productiveness  of 
any  soil  is  limited  by  the  amount  of  water  that  it  can  hold 
and  by  the  facility  with  which  it  yields  up  this  water  to 
growing  plants.  Soil  water  differs  from  rain  water  in 
that  it  contains  the  plant  foods  in  solution,  while  rain 
water  is  chemically  pure.  , 

Water  exists  in  soil  as  ground  water  which  drains  away, 
and  capillary  water  which  varies  with  the  kind  of  soil. 
The  finer  the  soil  particles  the  greater  the  amount  of  capil- 
lary water  or  film  water. 

Regulation  of  the  Amount  of  Soil  Water.  —  Soil  water 
may  limit  the  crop  by  being  present  in  either  too  great  or 
too  small  amounts.  Dry  farming  and  irrigation  are  prac- 
tical ways  of  obtaining  crops  in  regions  where  there  is  too 
small  an  amount  of  soil  water.  Commonly  there  is  too 
much  water  in  the  soil  in  the  early  part  of  the  season  and 
too  little  as  the  season  advances,  so  that  the  crop  is  injured 
by  both  extremes. 

When  there  is  too  much  water  in  the  soil,  air,  which  is 
essential  for  plant  growth,  is  excluded,  and  the  soil 
remains  cold.  This  retards  the  growth  of  the  plant  and 
delays  farm  work. 

Artificial  Drainage.  —  Underground  drainage  of  some 
sort  is  essential  for  the  growth  of  ordinary  crops.  Where 
the  soil  is  not  drained,  the  excess  of  water  prevents 
the  growth  of  crops,  and  where  there  is  no  excess  of 
water  to  drain  away,  the  soil  becomes  either  acid  or 
alkaline  due  to  the  accumulation  of  salts  and  acids, 


SURFACE  WATER,  DRAINAGE,  AND  IRRIGATION     311 


which  are  carried  in  solution  into  the  soil  by  the  surface 
water. 

Where  the  subsoil  is  porous,  natural  drainage  is  usually 
sufficient  to  remove  the  excess  of  water.  Where  the  sub- 
soil is  a  heavy  clay, 
artificial  drainage 
must  be  employed. 
Most  farms  can  be 
improved  by  tile 
drains  properly  lo- 
cated, and  many 
farms  need  a  com- 
plete system  of 
drains  laid  from 
two  to  six  rods 
apart.  (Figure 
267.) 

Tile  drains,  in 
addition  to  remov- 
ing  excess  soil 
water,  actually 
serve  .to  protect 
plants  in  times 
of  dry  weather. 
When  the  excess 
soil  water  is  quickly 
removed,  the  plant 
roots  grow  much 
deeper  than  in  soil  that  is  wet  and  cold.  These  plants 
with  deep  roots  are  then  able  to  withstand  considerable 
dry  weather,  since  the  roots  are  able  to  use  the  capillary 
water  of  the  subsoil. 

Irrigation.  —  About  two  fifths  of  the  total  area  of  the 


FIG.  267.  —  Tiling  Level  Lands,  Illinois. 


312 


GENERAL  SCIENCE 


United  States  receives  insufficient  rainfall  to  produce 
yearly  crops  without  irrigation.  In  some  parts  of  this 
area  occasional  crops  may  be  produced  by  dry  farming, 
but  this  means  that  only  a  small  fraction  of  what  the  land 
is  capable  of  producing  with  adequate  rainfall  will  be 
produced.  The  land  along  a  stream  is  always  more  fertile 
than  the  land  farther  away  from  the  stream.  In  some 


U.  S.  Reclamation  Service. 
FIG.  268.  —  Salt  River  Project,  Arizona.     The  Desert  Before  Reclamation. 

regions  it  has  been  possible  to  divert  part  of  the  water  of 
streams  through  canals  and  ditches  so  that  a  much  larger 
area  is  watered.  This  is  called  irrigation. 

In  the  western  part  .of  the  United  States,  especially  in 
the  region  west  of  the  Rocky  Mountains,  the  United  States 
Reclamation  Service  and  a  number  of  private  organiza- 
tions are  maintaining  a  number  of  irrigation  systems 
(Figures  268,  269).  The  engineering  problems  involved 


SURFACE  WATER,  DRAINAGE,  AND  IRRIGATION     313 

in  these  enterprises  are  enormous,  but  the  returns  have 
usually  justified  the  expense.  In  some  places  immense 
dams  are  necessary.  In  other  regions  miles  of  concrete- 
lined  canals  have  been  built.  The  large  storage  dams 
retain  the  water  that  falls  in  certain  stream  basins  during 
the  winter  and  early  spring  months.  As  this  water  is 


U.  S.  Reclamation  Service. 
FIG.  269.  —  Salt  River  Project,  Arizona.     The  Desert  After  Reclamation. 

needed  by  the  farmers  below  the  dam,  it  is  allowed  to  flow 
into  canals  which  carry  it  to  the  tract  to  be  watered. 

It  will  never  be  possible  to  irrigate  all  the  arid  land  in 
this  way,  since  the  total  amount  of  rainfall  of  the  dry 
region  is  only  enough  to  water  properly  one  tenth  of  it. 
Then  too,  some  sections  are  so  located  that  the 'expense 
of  bringing  water  to  them  would  be  too  great  to  make 
them  profitable. 


314  GENERAL  SCIENCE 

In  the  United  States  Government  irrigation  projects 
the  reclaimed  land  is  sold  to  settlers  at  a  price  which  more 
than  pays  the  cost  of  the  work.  The  money  thus  received 
is  used  in  the  construction  of  other  reservoirs  and  canals. 

Private  corporations  often  sell  the  water  to  users. 

QUESTIONS 

1.  What  conditions  determine  what  becomes  of  the  rain  when 
it  falls  to  the  ground? 

2.  What  work  is  done  by  the  water  that  sinks  into  the  ground  ? 

3.  What  is  an  artesian  well? 

4.  How  is  the  dissolving  power  of  soil  water  increased? 

5.  What  is  a  river  basin ?     A  divide? 

6.  What  are  the  characteristics  of  a  young  river? 

7.  Why  are  there  no  floods  at  Detroit? 

8.  Is  the  water  in  a  salt  lake  increasing  or  decreasing  in  density  ? 
Why? 

9.  Why  is  it  impossible  for  a  person  to  sink  in  Great  Salt  Lake  ? 

10.  What  are  some  of  the  peculiarities  of  rivers  in  dry  climates? 

11.  How  do  rivers  build  deltas?     Where? 

12.  If  the  velocity  of  running  water  is  doubled,  how  will  its 
carrying  power  be  affected  ? 

13.  What  kind  of  soil  bakes  hardest  in  the  sun? 

14.  What  crops  in  your  region  grow  best  on  wet  lands? 

15.  How  does  pressing  down  the  soil  affect  the  movement  of 
soil  water? 

16.  Is  it  a  good  thing  to  pack  the  ground  over  grains  of  corn  just 
planted?     Why? 

17.  What  causes  the  alkaline  soils  found  in  some  of  our  western 
states  ? 

18.  Why  are  wet  soils  cold? 

19.  How  may  the  seepage  in  irrigation  canals  be  lessened? 

20.  After  land  is  irrigated  why  should  it  be  tilled  ? 

21.  Why   do   irrigated   soils   become   alkaline?     What   is   the 
remedy  for  this? 


CHAPTER  XIX 

PLANTS 

Properties  of  Living  Matter.  —  Living  matter  has  quite 
a  complex  chemical  composition.  It  contains  the  ele- 
ments nitrogen,  carbon,  hydrogen,  oxygen,  sulphur, 
and  phosphorus.  Other  elements  are  usually  found  in 
living  matter  in  minute  quantities.  The  name  protoplasm 


FIG.  270.  —  Reproduction  in  a  Strawberry  Plant  by  Division. 

has  been  given  to  this  complex  combination  of  these  ele- 
ments. Life  occurs  only  in  protoplasm,  and  plants  and 
animals  are  largely  composed  of  it. 

Protoplasm  possesses  the  property  of  irritability  and 
responds  to  the  stimuli  of  light,  heat,  and  electricity. 
Sprouts  on  tubers  and  plants  in  dark  places  always  grow 
toward  the  light.  Leaves  turn  toward  the  source  of 
light. 

315 


316  GENERAL  SCIENCE 

Protoplasm  has  the  power  to  move  by  contraction. 
Plants  move  and  change  the  position  of  their  leaves,  while 
the  muscular  action  is  a  well-known  power.  Protoplasm 
also  has  the  power  of  taking  up  materials  that  it  can  use 
as  food  and  rejecting  those  materials  which  it  cannot  use. 
Protoplasm  breathes  oxygen,  eliminates  wastes,  and  has 
the  power  to  reproduce  its  kind  of  plant  or  animal 
(Figure  270). 

The  Living  Plant.  —  Plants  are  fed  by  the  elements 
that  they  take  from  the  soil  and  air.  From  these  elements 

they  build  all  the  various  com- 
plicated plant  structures  known 
as  flowers,  seeds,  roots,  and 
stems.  Each  part  of  the  plant 
has  its  own  particular  purpose 
and  is  correspondingly  built.  If 
the  plant  is  properly  fed  it  will 
FIG.  27i.  — A  sick  and  a  Well  develop  evenly,  but  if  the  soil  is 

lacking  in  some  of  the  essential 

plant  foods  the  plant  which  grows  on  it  will  be  weak 
(Figure  271). 

Cells.  —  A  cell  is  the  smallest  bit  of  living  matter  that 
can  exist  alone.  All  plants  and  animals  are  composed  of 
cells  which  are  separate  masses  of  protoplasm,  each  hav- 
ing a  nucleus  and  each  surrounded  by  an  envelope  called 
the  cell  wall.  Cells  vary  greatly  in  size.  Some  of  them 
may  be  seen  readily  with  the  unaided  eye,  while  others 
have  a  diameter  of  not  more  than  1/25000  of  an  inch. 
In  shape  they  vary  from  long  strings,  such  as  are  found 
in  the  cotton  fiber,  to  the  spherical  eggs  of  animals. 

Tissues.  —  Collections  of  similar  cells,  grouped  to  pro- 
duce some  particular  part  of  a  plant  or  animal,  are 
tissues.  Examples  of  tissues  are  woody  tissue,  pith 


PLANTS 


317 


tissue,  bony  tissue,  and  the  skin  covering  the  bodies  of 
animals. 

Organs.  —  Each  part  of  a  plant  or  animal  which  has 
a  special  work  to  do  is  called  an  organ.  Tissues  are  com- 
bined in  various  ways  to  produce  organs  such  as  leaves; 
roots,  and  veins  in  plants  and  the  many  organs  of  the 
human  body. 

Multiplication  of  Cells.  —  When  a  cell  reaches  its  max- 
imum size,  it  may  divide  into  two  cells,  each  containing 


FIG.  272.  —  Showing  the  Method  of  Cell  Division. 
Note  the  division  of  the  nucleus. 

half  of  the  nucleus  and  the  protoplasm  of  the  old  cell 
(Figure  272) .  These  new  cells  may  grow  to  maximum  size 
and  again  divide.  The  multiplication  of  cells  in  this  way 
is  the  usual  process  of  growth  in  plants  and  animals. 

Flowers.  —  Flowers  grow  on  the  higher  forms  of  plants 
at  a  comparatively  mature  stage  in  their  development 
(Figure  273).  The  flower  is  grown  for  the  purpose  of 
producing  other  similar  plants.  In  order  to  understand 


318 


GENERAL  SCIENCE 


the  process  of  reproduction  in 
flowering  plants,  it  is  necessary 
to  make  a  study  of  the  parts 
of  a  flower  (Figure  274).  The 
outer  whorl  of  the  leaf  parts 
of  a  flower  is  called  the  calyx 
or  cup  of  the  flower  (Figure 
275).  Each  division  of  the  calyx 
is  called  a  sepal.  These  are 
often  green  in  color.  The  next 
whorl  of  parts  just  inside  the 
calyx  is  called  the  corolla.  Each 
leaf  of  the  corolla  is  called  a 
petal.  These  parts  of  the  flower 
are  not  essential  for  the  pur- 
poses of  reproduction,  but  they 
are  the  parts  which  make  flow- 
ers so  attractive  for  decorative 

FIG.  273.  — A  Peach  Twig. 

purposes. 

The  essential  parts  of  the 
flower  are  the  stamens  and 
the  carpels.  Each  stamen 
consists  of  a  supporting  stalk 
called  the  filament.  The 
anther  is  the  enlargement 
at  the  end  of  the  filament 
(Figure  276).  The  pollen, 
which  resembles  yellow  pow- 
der, grows  in  the  anther. 

The  carpels  of  a  flower 
considered  collectively  are  FlG-  274.  — Diagram  showing  the 

„     ,   .,  ,    /T,.  rti-ri^N  Parts  of  an  Ideal  Flower. 

called  the  pistil  (Figure  277).      o  anther;  cor  carpeU.  ^  petal; 

A   Simple    pistil    has   but  One   s,  sepals ;  at,  stamens. 


PLANTS  319 

carpel  (Figure  278) ;   a  compound  pistil  has  more  than 

one  carpel.     In  the  base  of  the  pistil  is  a  bulblike  seed 

case  called  the  ovary.     This  contains  the 

ovules   or  eggs.      Above  the  ovary  is   a 

slender  stem  called  the  style,  and  at  the 

end  of  the  style  is  a  sticky  surface  called 

the  stigma. 

Pollination.  —  In  order  that  seeds  may 

be  produced,  it  is  necessary  that  pollen 

from  the   anthers   lodge    on   the   stigma. 

This  may  happen  in  several  ways.     The 

anthers  of  some  flowers  burst  when  ripe    FIG.  275.  — Calyx 

and  scatter  the  pollen  on  the  stigma.    The       and  Corolla. 

wind  may  blow  the  pollen  so  that  it  falls  on  the  stigma. 

Insects  flying  from  one  flower  to  another  often  carry 
pollen  from  the  anthers  of  one  flower  to 
the  stigma  of  another.  This  is  cross- 
pollination. 

Fertilization.  —  Each  pollen  grain  con- 
sists of  a  particular  cell  called  the  sperm 
cell.  When  the  pollen  grains  fall  on  the 
stigma,  they -are  held  by  the  sticky  sur- 
face. They  immediately  begin  to  grow, 
forming  tubelike  roots  which  grow  down- 
ward through  the  stigma  and  the  style 
into  the  ovary,  where  they  pierce  the 
ovule  and  reach  the  egg  cell.  The  sperm 
cell  of  the  pollen  meets  the  egg  cell  of 
FIG  276  —Three  tne  OVU^Q  and  they  unite  to  form  a 

stamens  with  Differ-  single   cell,   which  grows  and  forms  an 

ent  Forms  of  Anther.  ,        ,    /TV  rM-rrv\         rrn 

embryo  plant  (Figure  279).  The  parent 
plant  stores  food  around  this  plant,  with  the  result 
that  fruits  and  seeds  are  formed.  The  fruits  are  simply 


320 


GENERAL  SCIENCE 


produced  by  nature  to  furnish  food  for  the  new  plants 
or  to  protect  the  seeds  from  climatic  conditions  until 
a  favorable  time  for  growth  shall  arrive. 

Dispersal  of  Seeds.  —  A  little  observa- 
tion will  disclose  to  any  one  a  number 
of  ways  in  which  seeds  are  dispersed. 
Hold  a  maple  seed  high  in  the  air  and 
notice  whether  it  falls  directly  to  the 
ground  or  not.  What  is  the  value  of 
wings  on  maple  seeds?  Some  seeds  like 
the  dandelion  and  thistle  are  provided 
with  little  parachutes  (pappus)  which 
FIG.  277.— stamens  enable  the  wind  to  carry  them  for  long 

and  Pistil.         distances  (Figure  280). 
Some  plants,   such  as  tumbleweeds,   break  from  the 
main   stem   and   are   then   blown    along   the 
ground,  scattering  seeds  as  they  go. 

Squirrels,  birds,  and  other  animals  are  active 
agents  in  the  dispersal  of  seeds. 

Germination  of  Seeds.  -  -  The  stages  passed 
through  by  a  young  plant  from  the  time  it 
begins  to  sprout  until  it  becomes  an  inde- 
pendent plant  are  called  germination. 

The  process  of  germination  may  be  studied 
by    planting    some    seeds   of    various   kinds. 
Plant   some  beans,   squash   seeds,   corn,  and 
wheat  in  warm,  moist  soil  or  sawdust  and  ob-  FIG.  278.  — A 
serve  them  from  day  to  day.      Some  of  each  simpleF 
kind  of  seeds  should  be  left  untouched  until  the  plant 
appears  above  the  surface  of  the  soil.     Do  they  all  come 
out  of  the  soil  in  the  same  way?     (Figure  281.) 

As  the  embryo  plant  in  the  seed  begins  to  grow,  it  again 
bursts  open  the  seed  leaves.     These  seed  leaves  contain 


PLANTS 


321 


starch  and  proteid,  which  are  so  changed  by  water  and 
the  digestive  ferments  ill  the  seeds  that  they  can  be  used 
as    food    by   the    growing   plant 
until  it  has  roots  capable  of  tak- 
ing   food    in    solution    from    the 
ground,    and    leaves    which   take 
the    carbon   dioxide   and   oxygen 
from  the  air  (Figure  282). 

Roots.  —  In  the  germination  of 
many  plants  the  roo't  grows  into 
the  soil  first,  to  get  water  and 
food  so  that  the  top  of  the  plant 
may  grow.  With  other  plants, 
however,  the  top  and  the  root 
seem  to  grow  simultaneously. 

There  are  several  factors  which 
determine  the  direction  taken  by 
roots.  Gravity  and  water  are  the 
most  important  of  these  factors 
(Figure  283).  Water  is  always 

found    below    the    Surface    Of    the  FlG-  279-  —  Fertilization  of  the 

earth,    but    sometimes    at    such 

depths  that  roots  must  go  long  distances  to  secure  a  supply. 
Many  plants  have  a  greater  area  of  root  surface  than  of 
branch  surface.  In  arid  regions  tree  roots  have  been 
known  to  penetrate  the  earth  to  a  depth  of  sixty  feet  in 
search  of  water. 


FIG.  2*80.  —  Seeds  of  the  Milkweed  Dispersed  by 
the  Wind. 


322 


GENERAL  SCIENCE 


Roots  serve  to  hold  plants  in  an  upright  position  and 
also  to  take  food  from  the  soil  by  the  process  of  osmosis. 
When  two  fluids  are  separated  by  a  porous  membrane  they 


FIG.  281. —  Development  of  the 
Bean. 

Note  how  the  seed  is  pushed  out 
of  the  ground,  the  formation  of  the 
seed  leaves,  and  the  withering  of 
the  seed  when  the  leaves  and  roots 
are  sufficiently  developed. 

intermingle  or  diffuse,  the  greater  flow 
being  toward  the  denser  medium.  The 
fluid  in  the  root  hairs  is  more  dense  than 
the  soil  water ;  therefore  the  soil  water 
bearing  plant  food  flows  into  the  roots 
faster  than  the  sap  flows  out,  and  the 
excess  fluid  is  forced  up  into  the  plant. 
This  action  takes  place  most  rapidly 
near  the  ends  of  the  roots  where  the 
root  hairs  are  most  numerous.  A  root  0  F.}?-  282;77A  „ 

Seedling  of  the  Castor 
hair   IS   really   a  living    plant    Cell    With    Bean,  Three  Weeks  Old. 

a  wall  so  thin  that  water  readily  passes      s''  s,te™ ;  r>  ,ro?ts ;  c' 

J  expanded    seed    leaves; 

through    into    the   interior  Of    the    root,    p,  permanent  leaves. 

Root  hairs  are  long,  hairlike  structures  almost  colorless 
in  appearance  (Figure   284).      They  are  probably  not 


PLANTS 


323 


larger  than  1/500  of  an  inch  in  diameter.  The  walls  are 
cellulose,  a  substance  which  readily  permits  the  passage 
of  fluids  through  it.  These  very  small  roots  take  the 


FIG.  283.  —  Distribution  of  Roots. 

food  from  the  soil,  while  the  larger  roots  carry  the  food 

to  the  stem  of  the  tree. 

Stems.  -  -  The  main  stem  of  a  plant  grows  in  a  direction 

opposite  to  that  of  the  first  root  of  a  seed,  while  the 
branches  from  the  main  stem  grow  outward 
in  a  way  quite  similar  to  the  root  branches 
.underground.  The  roots  grow  in  all  direc- 
tions to  get  food,  while  the  branches  from 
the  stems  grow  outward  to  get  light. 

Experiment  77.  —  Plant  some  grains  of  wheat 
or  oats  in  a  box  arranged  so  that  the  light  is  re- 
ceived from  but  one  side  (Figure  285).  Note  the 
direction  of  the  seedlings  as  they 'grow. 

Stems  serve  to  hold  the  leaves  in  a  posi- 
tion to  receive  light  and  air,  and  they  also 
furnish  a  pathway  for  the  food-bearing  liquid  which 
moves  from  the  roots  to  the  growing  parts  of  the  tree. 


FIG.  284.  —  Root 
Hairs. 


324 


GENERAL  SCIENCE 


FIG.    285.  —  Grains   of    Wheat 
Growing  Toward  the  Light. 


Stems  vary  in  structure.  In  corn  the  stem  or  stalk  is 
pithy  with  a  hard  rind  on  the  outside  and  numerous 

woody  fibers  running  length- 
wise through  it.  These  fibers 
and  the  rind  are  traversed  by 
minute  holes,  which  serve  as  a 
passageway  for  the  sap.  If  a 
longitudinal  section  of  the  stalk 
is  made,  some  of  those  little 
fibers  will  be  found  to  enter  the 
leaves  at  the  joints.  In  the 
leaves  they  appear  as  veins  and 
may  be  traced  readily.  The 
tough  woody  cells  of  the  rind 
furnish  the  main  support  of  the 
corn  stalk  as  it  matures. 

The  stem  of  the  ordinary  tree  contains  a  very  small 
pith  center.  Surrounding  the  pith  is  the  woody  fiber, 
which  is  composed  of  many  little  tubes  and  their  woody 
walls.  If  the  stem  is  several  years  old,  we  can  see  dis- 
tinct annual  rings  in  this  woody  part.  The  space  between 
two  consecutive  rings  indicates  the  growth  during  one 
summer  (Figures  286,  287).  Radiating  from  the  center 
of  the  stem  and  extending  to  the  bark  are  found  a  number 
of  tiny  lines.  These  lines  are  called  the  medullary  rays 
and  serve  as  storehouses  for  food  and  permit  the  flow  of 
sap  across  the  rings  of  the  tree.  These  rays  produce  the 
beautiful  effects  that  we  see  in  quarter-sawed  lumber. 

The  soil  water  that  is  taken  up  by  the  root  hairs,  under 
the  influence  of  osmotic  pressure  and  capillarity  (root 
pressure),  is  carried  by  the  minute  tubes  in  the  stems  to 
all  parts  of  the  plant  or  tree.  In  a  large  tree  most  of  the 
sap  is  carried  by  the  tubes  in  the  sapwood.  This  is  the 


PLANTS  325 

layer  of  white  wood  which  lies  immediately  under  the 
bark.  The  darker  heart  of  the  tree  is  composed  of  dead 
fibers  and  serves  as  a  storehouse  for  food  and  as  a  support 


Oak.  Cypress.  Southern  pine. 

FIG.  286.  —  Wood  Grains. 

for  the  other  parts  of  the  tree.  The  heart  of  the  tree 
is  most  valuable  for  lumber,  since  it  has  a  richer  color 
and  decays  slower  than  sapwood. 

The  bark  is  the  outer  portion  of  the  woody  stem.     The 
part  of  the  bark  which  is  next  to  the  sapwood  is  a  living 


FIG.  287.  —  Curly  Walnut,  Showing  Grain  in  the  Wood. 


326  GENERAL  SCIENCE" 

tissue  and  is  called  the  cambium  layer.  All  the  growth 
of  our  hardy  trees,  such  as  the  oak  and  maple,  takes  place 
from  the  cambium  layer.  It  forms  new  wood  on  the 
inside  and  coarse  bark  on  the  outside.  The  outside  bark 
of  a  tree  is  dead  and  serves  only  to  protect  the  tree  in 
various  ways. 

Leaves.  —  As  soon  as  a  seed  germinates,  leaves  are 
formed  on  its  stem.  Some  plants,  such  as  the  bean  and 
the  squash,  have  two  seed  leaves  which  appear  as  soon 
as  the  seed  has  swelled  in  the  process  of  germination. 
Leaves  are  essential  to  plant  life,  as  may  be  proved  by 
removing  the  leaves  from  a  young  plant. 

The  broad  part  of  a  leaf  is  called  the  blade  ;  the  stem  is 
called  the  petiole.  Leaves  may  be  classified  according 
to  the  arrangement  of  the  veins  (Figure  288).  Number 
1  shows  the  palmate-veined  leaf  of  the  maple ;  number 
2,  the  parallel- veined  leaf  of  the  wild  lily-of -the- valley ; 
number  3,  the  pinnately-veined  leaf  of  the  birch ; 
number  4,  the  pinnately  compound  leaf  of  the  rose. 
Veins  in  leaves  serve  the  double  purpose  of  supporting 
the  parts  of  the  leaf  and  of  furnishing  tubes  to  carry  food. 

In  almost  every  case  the  arrangement  of  the  leaves 
on  a  plant  is  such  as  to  secure  the  greatest  amount  of 
sunlight  for  them.  In  dense  forests  the  trees  grow  tall 
with  clusters  of  leaves  near  the  top,  while  in  open  fields 
the  same  species  of  tree  sends  out  numerous  lateral 
branches  covered  with  leaves.  On  the  smaller  plants 
the  leaves  arrange  themselves  in  various  ways,  but 
always  so  that  each  leaf  receives  a  large  amount  of  light. 

The  cells  of  a  leaf  are  composed  of  protoplasm  and  a 
green  material  called  chlorophyll.  The  layer  of  cells 
forming  the  upper  and  lower  part  of  the  leaf  is  called  the 
epidermis.  The  epidermis  on  the  upper  part  of  the  leaf 


PLANTS 


327 


has  slightly  thicker  walls  for  protection,  while  on  the 
under  side  it  is  pierced  by  numerous  pores  called  stomata. 
Many  thousand  of  these  openings  may  occur  in  a  square 


"K; 


1.    A  Maple  Leaf. 


4.    A  Rose  Leaf. 


2.   A  Wild  Lily-of-the- Valley  Leaf. 

FIG.  288. 


3.    A  Birch  Leaf. 


inch  of  leaf  surface.  The  stomata  are  the  lungs  of  the 
plant.  They  take  in  air  and  expel  gases  which  the  plant 
does  not  need.  Around  each  stoma  there  are  two  guard 


328 


GENERAL  SCIENCE 


a  c        c 

FIG.  289.  —  A  Section  of  a 


cells,  which  by  changing  their  shape  control  the  amount 
of  air  breathed  in  by  the  plant  and  also  the  amount  of 
evaporation  of  water  from  the  leaf  (Figure  289) . 

Starch   Making   by   Leaves.  —  The   leaves  also  serve 

as  a  factory  in  which  starch  and  sugar  are  manufactured. 

a  To  do  this  the  leaves  combine  water 

-— -+- and  carbon  dioxide.     Since  there  is 

more  oxygen  in  the  air  than  is  needed 
to  produce  the  carbohydrates,  starch 
and  sugar,  the  excess  oxygen  is 
breathed  out  by  the  leaves.  Thus 
plants  tend  to  purify  the  air  by 
exchanging  oxygen  for  the  carbon 
dioxide  in  it.  The  manufacture  of 
starch  and  sugar  in  the  leaf  is  car- 
ried on  by  the  chlorophyll  bodies 
Leaf.  within  the  leaves  under  the  influ- 

a,  epidermis;    b,  cells;    ence  of  the  energy  of  sunlight.    The 
sunlight  and  the  chlorophyll  bodies 
are  the  agents  in  the  production  of  these  carbohydrates, 
and  the  water  and  carbon  dioxide  are  the  raw  materials 
from  which  they  are  made. 

Plants  that  have  been  grown  in  the  dark,  and  plants 
that  lack  green  coloring  matter  (chlorophyll)  contain 
no  starch  or  sugar. 

Digestion  in  Plants.  —  Food  products  in  plants,  as  in 
animals,  may  require  changes  before  they  can  be  used  as 
foods.  Starch  is  a  food  for  plants,  but  it  is  quite  insoluble 
in  water  and  must  be  digested  before  it  can  be  used. 
This  is  accomplished  by  changing  the  starch  to  sugar, 
which  is  dissolved  by  the  water  and  carried  to  the  differ- 
ent parts  of  the  plant. 
Flowerless  Plants.  —  The  flowering  plants  are  the 


PLANTS  329 

highest  class  of  plants.  Their  composition  is  quite 
complex,  and  they  perform  the  functions  necessary  to 
their  life,  growth,  and  reproduction  in  complicated  ways. 
There  are  other  plants  which  do  not  have  flowers  and 
in  which  the  function  of  reproduction  is  accomplished  in 
other  ways  than  by  the  production  of  seeds.  Some  of 
these  plants  are  composed  of  but  a  single  cell,  which  per- 
forms all  the  functions  of  the  plant.  Reproduction  in 
such  plants  takes  place  when  the  cell  separates  into  two 
cells,  thus  forming  two  plants.  Higher  forms  of  flowerless 
plants  are  reproduced  by  spores  which  contain  a  very 
small  portion  of  protoplasm  capable  of  reproducing  its 
kind  of  plant.  For  convenience  in  study,  the  flowerless 
plants  may  be  divided  into  algae,  fungi,  mosses,  and 
ferns. 

Algae.  —  The  algae  are  the  lowest  form  of  plant  life, 
but  they  resemble  higher  plants  in  some  respects ;  they 
all  contain  chlorophyll  and  are  able  to  manufacture 
starch  from  water  and  carbon  dioxide.  Algae  vary  in 
size  from  simple  one-celled  plants  to  the  giant  kelp  of 
the  Pacific  Ocean,  which  frequently  attains  a  length  of 
several  hundred  feet.  A  common  alga  is  the  simple  one- 
celled  variety  that  is  frequently  found  on  the  bark  of 
trees  and  on  rocks.  It  has  a  greenish  color  and  may  be 
found  in  almost  any  forest. 

Pond  scum  is  another  alga  known  as  spirogyra.  It  can 
be  found  floating  on  the  surface  of  almost  any  stagnant 
pond.  The  cells  of  the  spirogyra  are  placed  end  to  end, 
so  that  they  form  long  threads.  It  is  heavier  than  water, 
but  enough  bubbles  of  oxygen  cling  to  the  masses  of 
threads  to  cause  them  to  float.  The  oxygen  is  given  off 
by  the  plants  as  starch  is  formed,  as  in  higher  plants. 
The  spirogyra  grows  by  a  division  of  cells  and  also  pro- 


330 


GENERAL  SCIENCE 


duces  a  spore,  which  is  formed  by  the  growing  together  of 
two  cells  to  form  one  strong  cell.  This  spore  cell  may 
remain  dormant  for  considerable  time  and  also  be  sub- 
jected to  extremes  of  heat  and  cold  without  destroying 
its  vitality. 

Fungi. — We  are  probably  familiar  with  the  toadstool 
and  the  edible  mushroom  (Figure  290).     These  plants  con- 


FIG.  290.  —  Tree  Trunk  Showing  a  Bracket  Toadstool. 

tain  no  green  coloring  matter  or  chlorophyll  and  so  cannot 
manufacture  starch  from  water  and  carbon  dioxide.  They 
are  members  of  a  large  plant  group  called  fungi.  Such 
plants  commonly  are  dependent  upon  decaying  animal 
and  vegetable  matter  for  their  food.  However,  some  of 


PLANTS 


331 


them  live  on  the  juices  of  living  plants.  Those  that 
feed  on  living  plants  are  called  parasites,  while  those 
that  live  on  decaying  matter  are  called 
saprophytes  (Figure  291).  Other  com- 
mon fungi  are  molds  and  yeasts. 

Molds  are  little  plants  that  grow  on 
many  organic  substances.  To  study  the 
growth  of  mold  we  have  only  to  moisten 
some  bread  and  cover  it  to  prevent  evap- 
oration. The  mold  spores  on  the  bread 
germinate  and  produce  both  root  and 
stem  threads,  on  which  black  knobs  full 
of  ripe  spores  soon  appear.  These 
spores  are  blown  about  by  currents  of 
air. 

Yeast    plants    are    simply    one-celled 
fungi  (Figure  292).     They  are  useful  as 
manufacturers    of    carbon    dioxide,     to  dew,   Caused  by  a 
raise  bread,  and  in  the  fermentation  of  Parasitic  Fungus" 
grains   and   fruit   juices.     In  the  production  of   carbon 
dioxide  by  yeast  plants,  sugar  is  changed  to  alcohol. 

Another  group  of  the  fungi  are  the  bacteria.      Some  of 
these  are  parasitic  to  man  and  produce  human  diseases  such 

as  typhoid  fever,  diphtheria, 
and  tuberculosis  (Figures  293, 
294).  However,  many  of  the 
bacteria  are  very  useful  (Figure 
295).  They  cause  milk  to  sour 
and  enable  us  to  make  cheese 

FIG.  292.  —  Growing  Yea'st  Plants. 


FIG.  291.  — A  Wil- 
low Attacked  by  Mil- 


decay  of  organic  matter  and  so  change  it  that  it  can 
be  used  as  food  for  plants.  They  attach  themselves 
to  the  roots  of  plants  and  help  to  produce  proper  food 


332 


GENERAL  SCIENCE 


ducing    Diph- 
theria. 


a 


for  them.  Bacteria  on  the  roots  of  clover,  peas,  alfalfa, 
and  similar  plants  take  nitrogen  from  the  air  and  convert 
it  into  plant  food.  Most  plants  require  some 
particular  kind  of  bacteria  for  proper  growth. 
Food  may  be  protected  from  destructive  bac- 
teria by  sealing  it  or  by  using  as  a  preserva- 
tive some  substance  in  which  the  bacteria 
cannot  grow. 

Mosses  and  Ferns.  —  Mosses  and  ferns  are 
plants  of  higher  development  than  the  algae 
and  fungi.  They  contain  chlorophyll  bodies,  and  there- 
fore are  able  to  manufacture  starch. 

Mosses  will  grow  in  extreme  climates  with  little  soil, 
and  therefore  have  probably  had  con-  ^A 

siderable  part  in  the  formation  of  soil 
from  rocks. 

Ferns  form  a  class  of  plants  slightly 
higher  than  mosses.  True  ferns  grow 
best  in  damp,  shady  places.  They 
flourish  in  the  densely  wooded  regions 
of  the  tropics,  where  they  grow  to 
immense  sizes  (Figure  296). 

The  reproductive  organs  of  the 
common  ferns  are  called  sori. 
They  appear  as  little  brown  dots 
on  the  under  surface  of  the  leaf. 
Distribution  of  Plants.  —  The 
distribution  of  plants  over  the 
earth's  surface  is  determined  by 
the  soil  and  the  climate.  It  some- 
times happens  that  a  soil  is  rich 
enough,  but  the  climatic  con- 

FIG.  295.  —  Bacteria  from  a          ...  . 

Healthy  Mouth  Magnified.       ditions  are  unfavorable   to   the 


FIG.  294.  —  a,  Bac- 
teria of  Pneumonia. 
b,  Bacteria  of  Tuber- 
culosis. 


333 


334  GENERAL  SCIENCE 

growth  of  certain  plants.  The  region  may  be  too  cold,  too 
hot,  too  wet,  or  too  dry  for  the  development  of  a  certain 
plant.  Some  of  our  common  grains  cannot  grow  in  the 
dry  soil  of  the  southwestern  states  where  the  giant  cactus 
thrives.  In  the  frigid  zone,  only  mosses  and  lichens  grow. 
From  the  Arctic  circle  to  the  equator  the  vegetation  differs 
widely.  In  the  colder  part  of  the  temperate  zone,  cone- 
bearing  evergreen  trees  are  found.  Farther  south,  in 
the  same  zone,  are  deciduous  trees  such  as  the  beech, 
maple,  oak,  and  chestnut ;  while  in  the  tropics  are  found 
the  mahogany,  cypress,  and  many  varieties  of  palms. 

QUESTIONS 

1.  Why  is  food  essential  to  living  matter? 

2.  When  a  plant  is  placed  in  water  it  will  live  for  a  while.     What 
determines  the  length  of  time  it  will  live  ? 

3.  Why  do  seeds  not  germinate  if  the  ground  is  too  wet? 

4.  What  are  the  conditions  necessary  for  seed  germination? 

5.  Is  light  necessary  for  germination? 

6.  Name  some   plants  whose   seeds   are   dispersed   by  winds. 
By  animals. 

7.  Which  develops  first,  the  root  or  the  stem  of  a  plant? 

8.  Why  do  roots  grow  down? 

9.  Name  three  commercial  uses  of  bark. 

10.  What  is  meant  by  "  quarter-sawing?  " 

11.  From  where  does  the  water  come  that  is  evaporated  from 
the  leaves? 

12.  Is  it  essential  that  a  plant  lose  water  by  evaporation  from 
its  leaves? 

13.  Name  three  functions  of  leaves. 

14.  Is  there  any  starch  in  toadstools  and  mushrooms?     Why? 

15.  Potato  sprouts  which  grow  in  a  dark  cellar  are  white.     Why? 

16.  When  are  molds  and  yeasts  harmful? 

17.  How  do  yeast  plants  cause  bread  to  rise? 

18.  How  do  plants  prepare  food?     From  what  materials? 

19.  What  is  the  effect  of  cultivation  on  plants? 


CHAPTER  XX 
PLANTS   FROM   AN   ECONOMIC   STANDPOINT 

The  Value  of  Trees.  —  Trees  are  valuable  to  mankind 
in  many  ways.  They  form  a  protective  covering  for  a 
part  of  the  earth's  surface ;  they  prevent  erosion  by 


Forest  Service,  Washington,  D.  C. 
FIG.  297.  —  Erosion  of  Unwisely  Cleared  Slope,  Western  North  Carolina. 

surface  water;  they  help  to  retain  the  moisture  in  the 
soil  by  keeping  the  soil  loose  and  lessening  evaporation ; 
they  furnish  valuable  commercial  and  food  products 

335 


336 


GENERAL  SCIENCE 


and  they  make  city  and  country  much  more  healthful 
and.  beautiful  places  in  which  to  live. 

Trees  as  a  Protective  Covering  for  the  Earth.  —  The 
soil  in  a  forest  is  of  such  a  nature  that  it  acts  like  a  sponge 
in  absorbing  a  large  amount  of  water.  The  soil  is  held 
in  place  by  the  roots  of  the  trees,  while  the  foliage  of  the 
trees  prevents  the  evaporation  of  water  from  the  soil. 
When  the  forests  are  removed,  surface  erosion  takes  place 


Forest  Service,  Washington,  D.  C. 

FIG.  298.  —  A  Portion  of  an  Old  Sale  Area  Cut  too  Heavily  and  Later  Badly 
Windblown.  The  Timber  is  Lodgepole  Pine,  Medicine  Bow  National  Forest, 
Wyoming. 

much  more  rapidly  (Figure  297).  If  observations  are 
made  while  traveling  in  almost  any  part  of  the  United 
States,  evidences  of  such  erosion  will  be  seen.  Sidehills 
will  be  marked  with  deep  gullies  made  by  the  surface 
water  as  it  runs  off  after  rains.  Often  streams  that  were 
never  dry  when  the  region  was  covered  with  trees 
remain  dry  several  months  in  the  year  after  the  trees 
have  been  removed. 


PLANTS  FROM  AN  ECONOMIC  STANDPOINT      337 

Uses  of  Wood.  —  The  forests  of  the  United  States 
have  an  area  of  approximately  1,000,000  square  miles, 
but  we  are  rapidly  decreasing  this  area  by  cutting  the 
trees  for  the  use  of  their  wood.  Millions  of  dollars  worth  of 
timber  in  the  United  States  have  been  wasted  by  careless 
owners  and  wasteful  methods  of  lumbering,  and  we  are 
just  beginning  to  take  an  interest  in  a  reasonable  preser- 
vation of  our  forests  (Figure  298).  In  the  southern  states 


Forest  Service,  Washington,  D.  C. 

FIG.  299.  —  A  Forestry  Map. 

are  vast  forests  of  yellow  pine  and  cypress.  In  Michigan, 
Wisconsin,  Minnesota,  and  the  northern  states  of  New 
England  are  forests  of  pine  and  spruce.  In  the  Appala- 
chian region  are  forests  of  hardwood,  including  oak,  chest- 
nut, beech,  and  maple.  On  the  Pacific  slope  are  forests  of 
pine,  Douglas  fir,  spruce,  and  redwood  (Figure  299). 

In  many  countries  of  Europe  the  forests  are  a  national 
care,  and  the  cutting  of  trees  is  prohibited  except  under 
certain  restrictions.  Each  year  our  own  government 


338 


GENERAL  SCIENCE 


spends  an  increased  amount  of  money  in  Forest  Service 
to  guard  against  the  possibility  of  fires  and  wasteful 
lumbering  (Figure  300). 

Wood  is  useful  for  fuel,  for  building  purposes,  in  the 
production  of  wood  alcohol,  for  making  charcoal,  for 
paper  pulp,  for  furniture,  and  various  other  purposes. 


Forest  Service,  Washington,  D.  C. 

FIG.  300.  —  Cut-over  Area  on  which  Regulated  Cutting  has  been  Observed, 
as  Shown  by  the  Brush  Piles  Ready  for  Burning,  the  Low  Stumps,  etc. 

As  a  fuel  it  is  still  used  in  many  parts  of  the  world. 
Where  the  waste  from  the  cutting  of  lumber  can  be 
utilized,  it  is  cheaper  than  most  fuels. 

As  a  building  material  wood  has  an  endless  number  of 
uses,  ranging  from  heaviest  construction  work  to  the  most 
delicate  cabinet  work.  Some  woods  are  particularly 
adapted  for  certain  purposes.  Pine  is  used  for  all  building 
purposes ;  cedar  is  used  for  shingles ;  cypress,  for  work 


PLANTS  FROM  AN  ECONOMIC  STANDPOINT      339 


which  is  exposed  to  weather ;  basswood,  for  work  demand- 
ing lightness ;  ash,  where  strength,  lightness,  and  straight 
grain  are  desired;  oak,  cherry,  mahogany,  rosewood, 
and  walnut  for  furniture ;  and  so  on  through  the  large 
list  of  woods. 

Trees  also  furnish  a  number  of  other  valuable  products, 
such  as  turpentine,  resin,  tar,  creosote,  cork,  maple 
sirup,  and  some  acids  and  oils. 

Other  Uses  of  Trees.  —  It  is  gratifying  to  note  the 
increased  attention  which  our  cities  are  giving  to  the 
question  of  trees.  In 
a  large  number  of  our 
cities  we  have  park  com- 
missions, and  in  a  few 
cities  we  have  city  for- 
esters whose  duties  are 
to  look  after  the  planting 
and  protecting  of  trees 
(Figure  301 ).  Some  rea- 
sons wThy  trees  should 
be  planted  in  a  city  are  : 
they  purify  the  air  ;  they 
enhance  property  values ; 
they  make  the  city  more 
beautiful ;  they  cool  the 
air  in  summer  by  the  FIG.  301.  — A  Good  Example  of  Tree 
evaporation  of  moisture 

from  their  leaves  ;  they  provide  shade  for  lawns  and  pave- 
ments ;  they  attract  birds ;  they  have  an  educational  and 
patriotic  influence  upon  the  citizens. 

Food  Plants.  —  Nearly  all  our  food  comes  directly 
or  indirectly  from  plants.  Sometimes  it  is  the  root  we 
eat,  sometimes  the  stem,  sometimes  the  leaves,  the 


340 


GENERAL  SCIENCE 


fruits,  or  the  seeds.  Even  the  meats  we  eat  come  in- 
directly from  plants,  for  they  come  from  animals  that 
feed  on  plants. 

Among  the  common  roots  that  are  used  by  man  are 
radishes,  beets,  parsnips,  carrots,  and  sweet  potatoes. 
Celery  and  potatoes  are  stems  used  as  foods,  while  cab- 
bage, lettuce,  spinach,  and  onions  are  examples  of  leaves 
used  as  food. 

Fruits  and  seeds  are  the  most  important  foods  of  man. 
The  ease  with  which  grains  may  be  stored  and  kept  for 


Ohio  Agricultural  Experiment  Station. 


FIG.  302.  — Cultivating  Corn. 

future  consumption  adds  greatly  to  their  value  as  foods. 
Corn,  wheat,  and  rice  are  the  three  most  important  grain 
foods  of  the  world,  while  barley,  rye,  and  oats  are  ex- 
tensively cultivated  for  use  as  foods  (Figure  302). 

Textile  Plants.  —  Cotton  is  the  world's  most  important 
textile  plant  (Figure  303).  It  requires  a  long  season  for 
maturing  properly  and  is  therefore  grown  only  in  warm 
climates.  Attached  to  the  seeds  are  long,  white  filaments 
which  are  manufactured  into  threads  and  cloth.  The 
cotton  seeds  furnish  an  oil  which  is  used  as  a  substitute  for 
olive  oil.  Other  plants  which  furnish  fibers  which  are  use- 
ful to  man  are  flax,  hemp,  and  jute.  Linen  cloth  is  made 


PLANTS  PROM  AN  ECONOMIC  STANDPOINT      341 


from  the  fibers  of  flax.  Flax  is  also  grown  for  its  seed, 
from  which  linseed  oil  is  made:  Hemp  has  a  coarse 
fiber  not  suitable  for  clothing.  Its  fibers  are  used  for 
loosely  woven  materials  such 
as  burlap,  and  also  for  ropes. 

Weeds. -- Weeds  are 
plants  that  have  little  or  no 
economic  value.  They  are 
plants  that  in  some  particu- 
lar place  are  not  wanted. 
In  a  garden  all  the  plants 
which  are  not  cultivated  as 
flowers  or  vegetables  are 
weeds.  In  a  tennis  court  all 
plants  are  weeds.  Most 
weeds  seem  to  be  unusually 
hardy.  They  possess  great 
ability  to  disperse  their  seeds 
and  to  resist  the  extremes  of 
climate  and  the  attempts  of  man  to  eradicate  them.  They 
flourish  in  poor  soil  and  in  fertile  soil.  They  preempt 
the  soil  and  absorb  the  plant  food  so  that  other  plants 
are  crowded  out  or  die  from  lack  of  food.  A  number  of 
weeds  are  so  persistent  in  their  growth  and  spread  so 
rapidly  that  the  United  States  Department  of  Agricul- 
ture has  classed  them  as  national  pests  and  has  adopted 
radical  measures  leading  to  their  extermination. 

Weeds  have  some  real  value.  They  help  to  make 
soil  and  to  renew  soils  in  worn-out  regions.  When  soil, 
through  poor  farming,  becomes  too  poor  to  grow  crops, 
weeds  will  still  grow  on  it  and  build  up  the  soil.  Weeds 
are  also  valuable  in  that  they  force  farmers  to  cultivate 
the  land. 


FIG.  303.  —  A  Cotton  Plant. 


342 


GENERAL  SCIENCE 


Some  few  plants  are  poisonous.  Probably  one  of  the 
best  known  of  these  is  the  poison  ivy,  a  three-leaved 
climbing  plant  which  attaches  itself  to  walls,  trees,  and 
fences  by  means  of  small  roots  growing  from  the  stem. 
Berries  from  wild  plants  should  not,  be  eaten  until  their 
identity  is  determined,  since  some  of  them  are  poisonous. 
Plant  Diseases.  —  Many  parasitic  fungi  live  on  useful 
plants  which  are  cultivated.  They  attack  trees,  grains, 

fruits,  and  vege- 
tables to  such  an 
extent  that  the 
damage  done  by 
them  annually 
amounts  to  mil- 
lions of  dollars, 
while  probably  as 
much  more  is 
spent  in  combating 
them.  The  most 
common  parasitic 
plants  are  rusts, 
molds,  smuts,  and 
blight-producing 
fungi. 

Wheat  Rust.  - 
For  many  years 
wheat  rust  ,  has 
been  one  of  the 
most  destructive 
and  most  dreaded  of  plant  diseases  because  it  destroys 
a  plant  upon  which  so  large  a  part  of  the  civilized  world 
is  dependent  for  food  (Figure  304) .  It  has  long  been  sus- 
pected but  only  recently  determined  beyond  a  doubt,  that 


U.  S.  Dept.  of  Agriculture. 
FIG.  304.  —  Wheat  Heads  and  Straw  Showing  Rust. 


PLANTS  FROM  AN  ECONOMIC  STANDPOINT      343 


the  parasite  passed  part  of  its  life  on  barberry  bushes  and 
then  transferred  its  place  of  living  to  the  wheat  plant. 
It  appears  on  the  wheat  leaves  and  stalks  as  a  collection 
of  reddish  brown  spots.  It  extracts  its  food  from  the 
leaves  of  the  wheat  plant,  which  is  so  weakened  that  no 
grain  is  produced.  Since  the  spores  germinate  readily 
only  on  the  bar- 
berry, the  remedy 
seems  to  be  to  de- 
stroy the  barberry. 
Rotation  of  crops 
aids  in  controlling 
this  disease. 

Brown  Rot.  - 
A  common  fungous 
disease  is  the 
brown  rot,  which 
attacks  stone 
fruits,  particularly 
plums  and  peaches. 
It  attacks  the  fruit 
on  the  tree,  its 
appearance  being 
marked  by  a.brown 
spot.  The  rotted 
fruit  falls  to  the 
ground,  or  shrivels 
and  clings  persis- 
tently to  the  tree  to  form  mummies  that  carry  the  disease 
over  the  winter.  In  the  spring  the  spores  which  develop 
in  countless  numbers  in  these  mummies  are  carried  by 
the  wind  to  the  tree  blossoms,  where  they  begin  their 
work  again.  The  disease  may  be  partially  controlled  by 


U.  S.  Dept.  of  Agriculture. 
FIG.  305.  —  Motor  Truck  Sprayer  in  Operation. 


344  GENERAL  SCIENCE 

burning  the  diseased  fruit  as  soon  as  it  appears  and  by 
spraying  early  with  Bordeaux  mixture  and  later  with 
lime-sulphur  (Figure  305). 

Pear  Blight  (Fire  Blight) .— Pear  blight  attacks  pear 
trees,  apple  trees,  and  occasionally  plum  trees.  It  is 
caused  by  bacteria  which  live  in  the  cambium  layer  just 
under  the  coarse  bark.  The  first  symptom  of  the  disease 
is  the  death  of  the  tips  of  the  tender  twigs.  The  leaves 
turn  yellow  and  then  dark  brown,  and  the  tree  seems  to 
be  dying  from  the  top  down.  In  driving  along  the  road 
one  may  often  see  orchards  affected  by  this  disease.  If 
neglected,  the  disease  will  spread  down  the  tree  and  to 
other  trees,  gradually  destroying  the  whole  orchard. 

The  diseased  limbs  should  be  removed  and  burned  as 
soon  as  they  are  detected,  but  something  more  than  this 
is  usually  necessary  to  eradicate  the  disease.  The  bac- 
teria move  down  the  tree  and  form  cankers  on  the  large 
limbs  and  on  the  body  of  the  tree.  Here  they  pass  the 
winter.  In  the  spring  these  cankers  exude  a  sticky 
liquid  containing  large  numbers  of  the  bacteria  which 
are  carried  to  the  flowers  and  other  parts  of  the  tree  by 
insects.  The  logical  point  of  attack  then  is  the  canker 
during  the  winter  months.  Remove  all  cankers  and 
scrape  the  diseased  parts.  Wash  the  wound  with  a  weak 
solution  of  corrosive  sublimate,  one  part  to  five  hundred 
of  water.  In  a  day  or  two  the  wound  should  be  painted 
with  lead  and  oil. 

Mildews.  -  -  The  downy  mildews  comprise  a  group 
of  fungi  which  have  been  very  destructive  to  cultivated 
crops.  Probably  the  most  destructive  mildew  is  that 
of  the  potato,  sometimes  called  late  blight.  The  mildew 
spores  are  always  present  in  the  atmosphere  in  the  summer 
time,  and  if  they  alight  on  the  potato  leaves  when  the 


PLANTS  FROM  AN  ECONOMIC  STANDPOINT      345 


proper  conditions  of  heat  and  moisture  are  present,  they 
produce  swarm  spores  that  soon  germinate,  each  one 
sending  out  a  slender  tube  which  enters  a  near-by  breath- 
ing pore  of  the  leaf.  Once  inside  the  leaf  they  grow 
rapidly  and  send  out  numerous  branches  which  absorb 
the  contents  of  the  cells  and  even  pass  down  through  the 
stalk  to  the  tubers  below.  Wherever  they  go  they  kill  the 
plant  cells  quickly, 
and  the  term  blight 
is  quite  applicable 
(Figure  306).  In 
a  few  days  the 
plants  of  the  whole 
field  may  present 
a  dry,  parched  ap- 
pearance, since  the 
roots  (mycelium) 
of  the  mildew  in 
the  leaves  send  out 
branches  which  de- 
velop millions  of 
spores.  These  may 
be  carried  by  the 
slightest  wind  to  other  parts  of  the  field.  This  fungus 
commonly  passes  the  winter  in  diseased  potatoes ;  hence 
great  care  should  be  taken  to  secure  good  seed  potatoes. 
Spraying  with  Bordeaux  mixture  will  prevent  the  spread 
of  the  disease. 

Other  mildews  attack  lima  beans,  onions,  citrous  fruits, 
grapes,  and  many  other  fruits  and  vegetables.  The  brown 
rot  of  the  grape  and  of  the  lemon  are  downy  mildews 
which  are  at  times  quite  destructive. 

Potato  Scab.  —  This  fungous  disease  attacks  potatoes 


U.  S.  Dept.  of  Agriculture. 

FIG.  306.  — Advanced  Stage  of  Early  Blight  on 
Potatoes. 


346 


GENERAL  SCIENCE 


and  may  do  much  damage  (Figure  308).     It  may  live  in 
the  soil  over  winter ;   in  such  cases  the  only  remedy  is  a 


U.  S.  Dept.  of  Agriculture. 
FIG.  307.  —  Suitable  Spraying  Outfit  for  a  Small  Orchard. 

rotation  of  crops.  If  the  soil  is  free  from  the  fungi,  the 
disease  may  be  avoided  by  soaking  the  seed  potatoes  for 
an  hour  in  a  solution  of  formaldehyde,  one  pound  of 

formaldehyde  to 
thirty  gallons  of 
water. 

Chestnut  canker 
is  a  fungous  plant 
which  was  only  re- 
cently introduced 
in  this  country, 
probably  from 

Japan  (Figure  309). 

As  the  plant   de- 


Ohio  Agricultural  Experiment  Station. 
FIG.  308.  —  Potato  Scab. 


PLANTS  FROM  AN  ECONOMIC  STANDPOINT      347 


velops,  millions  of  spores  are  produced,  which  are  blown 
about  by  the  wind.  When  they  alight  on  the  bark  of 
trees  and  sprout,  they  send  little  roots  into  .the  tree  and 
absorb  the  food  which  is  on  its  way  to  living  cells.  In  a 
short  time  the  tree  dies  from 
starvation.  The  only  remedy 
seems  to  be  the  removal  of 
infected  trees. 

Molds.  Experiment  78. — Make 
some  marks  on  a  piece  of  fresh 
bread  with  a  toothpick  that  has 
been  drawn  across  a  piece  of  moldy 
bread.  Now  put  the  piece  of  fresh 
bread  in  a  covered  can  or  under 
a  dish  away  from  the  light  and 
observe  it  from  day  to  day. 

Molds  develop  from  spores 
which  are  usually  present  in 
the  air.  When  these  spores 
fall  upon  a  moist  substance 
which  contains  suitable  food, 
they  send  out  fine,  rootlike 
threads  which  both  cover  and 
penetrate  the  surface  of  the  attacked  substance.  Mold 
will  grow  on  most  common  foods.  When  the  spores  fall 
on  a  jar  of  jelly,  they  germinate  if  the  temperature  is 
favorable,  and  soon  the  jelly  is  covered  with  a  layer  of 
gray  mold.  To  kill  the  mold  spores  it  is  only  necessary 
to  heat  the  food  to  a  temperature  of  90°  C. 

As  a  usual  thing  molds  are  destructive  and  render 
foods  unfit  to  eat.  However  certain  foods,  as  Roquefort, 
Camembert,  and  Brie  cheeses  depend  upon  the  molds 
for  their  characteristic  flavor. 


Ohio  Agricultural  Experiment  Station. 
FIG.  309.  —  Chestnut  Canker. 


348  GENERAL  SCIENCE 

Smuts.  —  Many  of  us  are  familiar  with  the  masses  of 
loose  black  or  dark  brown  powder  which  are  found  on  the 
heads  of  oats.  These  black  masses  are  composed  of  mil- 
lions of  minute  spores  of  a  fungus  known  as  oats  smut. 
These  spores  are  carried  through  the  threshing  process 
with  the  chaff  that  is  usually  mixed  with  the  grain.  When 
planted  with  the  oats,  they  germinate  and  enter  the 
young  oat  plant,  where  they  branch  in  various  directions 
with  the  growing  tissues  of  the  plant.  When  the  plant 
begins  to  "  head,"  the  smut  fungus  develops  a  mass  of 
small  threads  within  the  tiny  blossom.  These  threads 
soon  develop  the  countless  black  spores  that  form  the 
characteristic  powder  of  smut  as  we  see  it  on  oats.  Oats 
srnut  may  be  prevented  by  soaking  the  seed  in  a  dilute 
solution  of  formaldehyde.  Corn  and  onion  smuts  are 
quite  common  on  ground  where  the  crops  are  not  rotated, 
but  they  are  not  usually  very  troublesome. 

Black  knot  is  a  fungous  disease  which  affects  plum  and 
cherry  trees.  In  warm  weather  large  numbers  of  the 
spores  are  produced  on  these  knots.  These  spores  are 
carried  by  the  wind  to  other  trees,  where  they  are  likely 
to  germinate  and  start  the  disease. 

All  diseased  branches  and  badly  infected  trees  should 
be  cut  down  and  burned.  Spraying  diseased  parts  with 
fungicides  will  prevent  the  spread  of  the  disease.  (See 
Appendix  II.) 

Peach  leaf  curl  is  due  to  the  growth  of  a  parasitic 
fungus  which  enters  the  leaf,  causing  it  to  become  enlarged 
and  to  curl.  The  injured  leaves  fall  early  in  the  summer. 
Winter  spraying  with  Bordeaux  mixture  or  with  lime- 
sulphur  will  destroy  the  spores  of  this  fungus. 

There  are  other  fungous  plant  diseases  which  are  pecul- 
iar to  small  regions.  As  a  usual  thing  they  yield  easily 


PLANTS  FROM  AN  ECONOMIC  STANDPOINT      349 

to  treatment.  When  requested  to  do  so  the  State  Agri- 
cultural department  will  usually  furnish  pamphlets 
dealing  with  the  crop  pests  of  that  state  and  the  best 
methods  of  destroying  them. 

Yeast.  —  Man  has  learned  how  to  use  yeast  plants 
so  that  they  have  an  economic  value.  All  fermentation 
and  the  process  of  modern  bread  making  depend  upon  the 
yeast  plant. 

Experiment  79.  —  Add  a  fourth  of  a  cake  of  compressed  yeast 
cake  to  a  pint  of  water  containing  some  molasses  or  sugar.  Now 
divide  this  mixture  in  three  parts,  placing  each  part  in  a  small  jar. 
Cover  the  jars  and  place  one  of  them  on  ice.  Place  another  in  a 
moderately  warm  place,  and  put  the  third  in  a  water  bath  and 
subject  it  to  a  boiling  temperature  for  ten  minutes,  after  which 
place  it  near  the  second  jar.  Two  days  later  examine  the  jars. 
Have  any  bubbles  appeared  in  the  jars?  In  which  jar  or  jars? 
What  effect  has  heat  upon  yeast  plants?  What  effect  has  cold? 
Devise  an  experiment  to  determine  the  kind  of  gas  released  by 
yeast  plants.  What  does  baking  do  to  the  yeast  plants  in  bread? 

QUESTIONS 

1.  In  what  ways  do -trees  cool  the  atmosphere? 

2.  What  precautions  are  now  being  taken  to  prevent  forest  fires  ? 

3.  Cypress  lasts  better  when  not  painted.     Why? 

4.  Name  two  uses  of  the  maple  tree. 

5.  How  is  science  increasing  the  value  of  our  food  plants? 

6.  How  many  bushels  of  corn  were  grown  in  the  United  States 
last  year? 

7.  Where  is  hemp  grown? 

8.  Name  ten  weeds. 

9.  How  do  fungi  differ  from  common  plants? 

10.  How  do  spores  differ  from  seeds? 

11.  What  are  the  worst  plant  diseases  of  your  region  \ 

12.  Name  some  other  plant  rusts  besides  wheat  rust. 


CHAPTER  XXI 

ANIMAL   LIFE 

Relation  of  Plants  to  Animals.  -  -  The  simplest  plants 
are  composed  of  a  single  cell.  The  simplest  animals 
also  are  composed  of  a  single  cell.  Both  plants  and 
animals  possess  the  power  of  irritability ;  both  have  the 
power  to  change  their'  position ;  and  both  possess  the 
power  of  reproduction.  The  elements  necessary  to  the 
growth  of  plants  and  animals 'are  all  found  in  the  soil, 
the  air,  and  the  water.  There  is  a  difference  however 
between  plants  and  animals.  Animals  do  not  have  the 
power  of  making  their  own  foods  from  the  elements  found 
in  the  soil,  air,  and  water,  but  are  dependent  upon  plants 
for  certain  essential  foods.  Animals  require  green  plants. 
The  protoplasm  of  green  plants  reacting  under  the  in- 
fluence of  sunlight  manufactures  food  which  is  used  by 
both  plants  and  animals.  Whether  an  animal  is  herbiv- 
orous, eating  plants  only,  or  carnivorous,  eating  flesh 
only,  its  food  can  be  traced  to  the  same  source.  Animals 
that  eat  both  plant  and  animal  flesh  are  called  omnivorous. 

In  the  scale  of  animal  life  we  have  many  gradations 
from  the  simplest  one-celled  animal  to  man,  the  highest 
type  of  vertebrate.  Between  these  two  extremes  we  have 
such  animals  as  worms,  oysters,  snails,  lobsters,  insects, 
fishes,  reptiles,  birds,  and  animals  like  the  horse. 

One-celled  Animals.  —  Amoebae  are  one-celled  animals 
which  may  be  obtained  for  purposes  of  study  from  vege- 
tation growing  near  the  surfaces  of  ponds.  Unlike  other 

350 


ANIMAL  LIFE 


351 


cells  we  have  studied  they  have  no  fixed  form  but  have  the 
appearance  of  an  irregular  mass  of  protoplasm  which 
changes  in  form  constantly  as  it  moves  about. 

There  are  no  separate  organs  in  these  animals.     The 
one  cell  performs  all  the  functions  necessary  to  their 


FIG.  310.  —  Amoeba  Showing  Division. 

life.  Reproduction  takes  place  by  a  division  of  the  cell 
into  two  cells  (Figure  310).  In  the  amoeba  any  part  of 
the  cell  seems  to  be  able  to  perform  all  its  functions,  such 
as  absorbing  food  and  oxygen  and  excreting  waste  material 
(Figure  311).  Slightly  higher  forms  of  single-celled 
animals  have  a  mouth  through  which  food  is  taken. 

If  a  small  bunch  of  hay  is  placed  in  a  glass  jar  nearly 
filled  with  water  and  allowed  to  stand  for  a  few  days  in  a 
warm  room,  certain  changes  will  be  noticed  in  the  con- 
tents of  the  jar.  An  unpleasant  odor  indicates  that  the 


FIG.  311.  —  The  Way  an  Amoeba  Gets  its  Food. 

hay  is  decaying ;  a  bacterial  scum  appears  on  the  surface 
of  the  water ;  a  little  later  small  one-celled  animals 
appear  in  this  scum  in  such  quantities  that  the  surface 
of  the  water  seems  literally  alive  with  them.  These 


352 


GENERAL  SCIENCE 


FIG.   312. —  A  Para- 
mecium. 


little  animals  must  of  course  come  from  the  water,  the 
air,  or  the  hay.  They  were  there  in  a  dormant  state. 
We  simply  adjusted  conditions  so  that 
these  were  favorable  to  their  develop- 
ment. Such  an  animal  is  called  a  para- 
mecium  (plural  paramecia)  (Figures  312, 
313).  It  is  a  more  complex  organism 
than  the  amoeba.  Under  the  microscope 
it  is  seen  to  have  a  somewhat  regular 
shape,  to  have  the  power  of  moving  itself 
by  means  of  special  parts  of  its  cell, 
called  cilia,  and  to  take  its  food  through 
a  definite  opening  or  mouth. 

Division  of  Labor.  —  As  we  observe 
animals  higher  in  the  scale  of  life  we  find 
that  certain  parts  of  animals  have  a 
definite  work  to  do.  A  part  of  a  plant  or  animal  which 
has  a  special  work  to  do  is  called  an  organ.  Thus  we  have 
organs  that  take  food ;  organs  that 
digest  food ;  organs  for  the  circula- 
tion of  blood  and  other  fluids ; 
organs  of  breathing ;  organs  of  ex- 
cretion ;  organs  of  voluntary  move- 
ments ;  organs  of  special  senses ; 
nerve  organs ;  organs  of  reproduc- 
tion ;  and  organs  of  protection. 
The  refinements  in  the  functions  of 
the  various  organs  of  an  animal 
determine  its  position  in  the  scale 
of  life,  just  as  the  degree  of  the  de- 
velopment of  the  principle  of  "  divi- 
sion of  labor  "  determines  the  civili- 
zation Of  a  people.  FIG.  313.  — Paramecia. 


ANIMAL  LIFE 


353 


BASE 
FIG.  314.  — The  Hydra. 


Hydra.  —  The  hydra  is  a  fresh-water  animal  which 
resembles  a  hollow  bag.  Food  is  carried  into  the  animal 
by  little  tentacles  which  grasp  the  food  and  carry  it 
toward  the  mouth  (Figure  314). 
The  body  wall  of  the  hydra  is 
made  up  of  two  layers  of  cells. 
The  inner  layer  serves  to  digest 
the  food,  while  the  outer  layer 
serves  as  a  protective  covering 
for  the  inner  layer.  Between 
these  two  layers  of  cells  are  some 
muscular  fibers  and  nerve  cells 
which  enable  the  animal  to  re- 
ceive sensations  and  to  move  the 
parts  of  its  body,  or  to  change  its 
position. 

Worms.  —  Earthworms  must  be  classified  among  our 
most  useful  animals  (Figure  315).  They  break  up  the 
soil,  thus  allowing  water  and  air  free  passage  through  it. 
They  also  carry  large  quantities  of  deep  soil  to  the  surface, 
thus  mixing  the  soil  and  making  it  more  fertile.  The 
damage  they  do  to  growing  plants  is  small  compared  with 

the  good  they  do 
in  the  soil. 

Earthworms  fur- 
nish an  interesting 
laboratory  study. 
They  may  be  kept 
for  some  time  in  a 

box  filled  with  soil.  Notice  how  the  worm  moves.  It 
has  two  layers  of  muscles  which  provide  for  its  move- 
ments :  an  outer  layer  which  passes  in  a  circular  direction 
around  the  body,  and  another  longitudinal  set  which  runs 


FIG.  315.  —  An  Earthworm. 


354  GENERAL  SCIENCE 

the  length  of  the  body.  The  body  is  shortened  by  the 
contraction  of  the  muscles  running  lengthwise  and 
lengthened  by  the  contraction  of  the  circular  muscles. 
In  moving  the  worm  extends  its  head  and  then  shortens 
its  body  by  contraction  of  the  longitudinal  muscles. 
Why  doesn't  the  head  slip  back  as  these  muscles 
contract  ? 

Examine  the  under  surface  of  an  earthworm  with  a  good 
lens.  How  are  these  anchors  used?  The  worm  has  no 
eyes,  yet  it  is  quite  sensitive  to  light.  How  can  you  test 
it  to  determine  whether  it  likes  light  or  darkness? 


MOUT 


FIG.  316.  —  The  Food-tube  of  an  Earthworm. 

These  worms  get  their  food  from  plants  and  from  .the 
soil  which  passes  through  their  bodies.  They  are  able  to 
burrow  into  very  hard  soil.  This  they  do  by  literally 
eating  their  way  through  (Figure  316). 

The  earthworm  has  a  nervous  system  with  a  well- 
developed  sense  of  touch.  It  also  has  a  blood  circulation. 
It  has  no  lungs,  the  skin  acting  as  an  organ  of  breathing. 
To  facilitate  the  passage  of  air  (osmosis)  the  skin  of  the 
worm  is  kept  moist  by  a  secretion.  During  heavy  rains 
the  worms  often  come  to  the  surface,  because  as  the  ground 
becomes  soaked  they  are  covered  with  water  and  cannot 
get  sufficient  oxygen.  There  are  many  other  kinds  of 
worms,  but  the  earthworm  is  typical  of  the  whole  class. 

We  must  be  careful  not  to  confuse  caterpillars,  grubs, 
and  similar  larvae  with  worms.  Worms  retain  their 


ANIMAL  LIFE  355 

identity  through  life,  while   the  larvae  simply  represent 
a  stage  in  the  development  of  insects. 

Insects.  —  All  insects  have  six  legs  in  their  mature 
stage.  This  feature  distinguishes  them  from  crustaceans, 
which  always  have  more  than  six  legs,  usually  ten,  the 
spiders,  which  have  eight  legs,  and  from  the  centipedes, 
which  have  many  legs.  Insects  have  bodies  which  are 


FIG.  317.  —  Stages  in  the  Development  of  the  Fly. 

divided  into  three  parts:  the  head,  the  thorax,  and  the 
abdomen.  They  breathe  air  directly  by  means  of  air 
tubes  or  trachea,  which  permeate  all  parts  of  the  body 
cavity. 

Insects  like  the  common  house  fly  pass  through  four 
different  periods  in  their  development.  The  female  may 
lay  from  one  hundred  to  two  hundred  eggs.  From  these 
eggs  the  maggots  or  larvae  hatch  (Figure  317).  After  a 
few  days  of  feeding  these  maggots  go  into  the  pupal 
stage.  In  about  one  more  week  the  adult  fly  emerges 


356 


GENERAL  SCIENCE 


(Figure  318).  The  adult  fly  breeds  at  once.  Since  the 
whole  cycle  from  egg  to  fly  requires  but  two  weeks,  it  is  easy 
to  account  for  the  large  number  of  flies  in  late  summer. 

Fortunately  most  of  them  are 
killed  by  the  winters  of  the 
temperate  regions. 

Insects  form  by  far  the 
largest  class  of  animals. 
Some  of  them  are  valuable, 
but  many  of  them  are  de- 
structive and  live  at  the 
expense  of  valuable  plants. 
Typical  insects  are  the  locusts 
or  short-horned  grasshoppers, 
the  butterflies,  the  moths,  the 
beetles,  the  cicadse,  the  bees, 
ants,  and  wasps. 

Bees  and  Ants.  —  From 
the  social  standpoint  these 
insects  are  very  interesting. 
They  seem  to  have  worked 
out  a  scheme  for  community 
life  which  provides  for  a  gov- 
ernment and  a  division  of 
labor  (Figure  319). 
The  honeybee  is  the  most  interesting  individual  of 
this  class  of  insects.  In  their  wild  state  honeybees 
live  in  colonies  with  a  hollow  tree  for  a  home.  There 
are  three  kinds  of  bees  in  a  colony:  the  male  bees  or 
drones,  the  workers,  and  the  queen  or  female  bee  (Figure 
320).  If  it  is  possible  to  have  a  hive  of  bees  for  observa- 
tion, the  division  of  labor  may  be  easily  seen  and  studied. 
The  queen's  work  is  to  lay  all  the  eggs.  This  she  does 


FIG.  318.  — The  House  Fly,  Male 
(top)  ;  Female  (bottom). 


ANIMAL  LIFE 


357 


with  great  regularity  during  the  warm  weather,  sometimes 
laying  as  many  as  several  thousand  eggs  in  a  day.     Most 


FIG.  319.  —  Section  of  a  Bee  Farm. 


of  the  eggs  are  fertilized  by  the  sperm  cells  of  the  males. 
The  unfertilized  eggs  develop  into  males.     The  workers 


Queen 


Worker 
FIG.  320. 


Drone 


do  all  the  work  of  the  hive.     They  make  the  hcwiey  and 
the  wax  and  feed   the   larvae  or  grubs  as  they  hatch, 


358  GENERAL  SCIENCE 

on  food  which  has  been  partially  digested  in  their  own 
stomachs.  After  a  few  days  the  grub  is  given  a  supply 
of  food  and  sealed  in  a  cell  by  the  workers.  In  about  two 
weeks  it  breaks  out  as  an  adult  worker. 

When  a  new  queen  is  to  be  produced,  the  young  larva 
is  fed  during  the  whole  pupal  period  upon  the  special 
food  known  as  bee  jelly  and  grows  to  a  larger  size  than 
the  workers.  When  a  young  queen  appears,  the  workers 
usually  divide.  Some  of  them  remain  in  the  hive  with  the 
new  queen,  while  others  follow  the  old  queen  out  of  the 
hive.  If  the  old  queen  alights,  they  settle  around  her, 
forming  a  mass  of  bees.  This  is  called  swarming.  To 
prevent  them  from  leaving  it  is  necessary  to  provide 
new  quarters  for  them. 

The  queen  bee  may  live  for  several  years,  but  the 
workers  live  but  a  few  months.  The  drones  are  driven 
out  or  killed  by  the  workers.  If  bees  are  properly  cared 
for  and  provided  with  a  source  of  food,  they  will  produce 
enough  honey  to  be  quite  profitable.  Since  they  visit 
so  many  flowers,  they  are  also  valuable  as  carriers  of 
pollen. 

Fishes.  —  All  of  the  animals  we  have  studied  thus  far 
have  either  had  no  skeleton  or  have  had  an  exterior 
skeleton.  They  are  called  invertebrates.  There  are  five 
classes  of  animals  having  flexible  vertebral  columns  or 
backbones.  They  are  fishes,  amphibians,  reptiles,  birds, 
and  mammals.  Collectively  these  five  classes  are  called 
vertebrates. 

The  fish  is  an  animal  that  lives  in  the  water.  Most 
fish  are  protected  by  platelike  scales,  which  overlap  each 
other  in  such  a  way  as  to  leave  the  body  flexible.  The 
tail  fin  of  a  fish  is  the  principal  organ  of  motion,  although 
the  other  fins  all  have  something  to  do.  The  fin  on  the 


ANIMAL  LIFE  359 

back  keeps  the  fish  right  side  up,  while  the  side  fins  are 
used  in  steering. 

The  specific  gravity  of  a  fish  is  nearly  that  of  water. 
By  means  of  an  "  air  bladder  "  the  fish  may  increase  or 
decrease  its  volume  enough  to  cause  it  to  sink  or  rise  in 
the  water.  The  cartesian  diver  illustrates  this  principle 
admirably.  Fishes  breathe  by  means  of  gills  which  take 
oxygen  from  the  water.  The  fish  has  a  well-developed 
circulatory  system,  including  a  heart  with  two  chambers. 

Amphibians.  —  Amphibians  are  animals  that  live  both 
on  the  land  and  in  the  water,  as  the  name  indicates. 
"  Amphi  "  means  both  and  "  bia  "  means  life.  Common 
amphibians  are  frogs,  toads,  mud  puppies,  and  salaman- 
ders. In  the  primary  stages  of  their  development  these 
animals  breathe  in  oxygen  by  means  of  gills  Most  of 
them  undergo  a  complete  change  during  life.  Some  of 
them  develop  lungs  in  their  second  stage.  The  circulation 
is  of  slightly  higher  development  than  in  the  fish,  the  heart 
having  three  chambers,  two  auricles  and  one  ventricle. 

The  frog  is  an  amphibian  which  may  be  easily  studied. 
In  the  early  spring  the  frogs  lay  their  eggs  in  water.  In 


\  2  3  4~  |  5 

FIG.  321.  — The  Development  of  the  Frog. 

a  short  time  these  eggs  hatch  into  tadpoles.  Tadpoles 
resemble  fish  and  breathe  with  gills  as  fish  do.  As  the 
tadpole  develops,  legs  appear  on  the  body,  and  its  organs 
of  breathing  change  from  gills  to  lungs.  The  toad  tadpole 
develops  in  a  month  or  two  after  hatching,  but  the  frog 
tadpole  does  not  make  the  complete  change  to  a  frog  until 
the  second  summer  (Figure  321). 


360  GENERAL  SCIENCE 

Reptiles.  —  Reptiles  are  lung-breathing  vertebrates 
having  a  scaly  tough  skin.  Common  reptiles  are  snakes, 
turtles,  alligators,  and  crocodiles.  In  the  turtle  the  scaly 
covering  has  developed  into  a  bony  shell.  Reptiles  are 
related  to  birds.  They  reproduce  themselves  by  means 
of  eggs  which  they  lay  in  the  ground.  A  few  snakes  are 
poisonous.  In  the  United  States  the  most  dangerous 
are  the  rattlesnake,  the  copperhead,  and  the  water 
moccasin. 

Birds.  -  -  The  principal  characteristics  of  birds  are  their 
protective  covering  of  feathers  and  the  presence  of  wings. 
The  feathers  are  developed  from  the  skin  and  show  a 
variety  of  form  and  color.  The  bills  of  birds  also  exhibit 
a  variety  of  forms  adapted  to  the  ways  in  which  the  dif- 
ferent birds  get  their  food.  Birds  of  prey  have  a  hooked 
beak.  The  woodpecker  has  a  sharp  straight  bill.  Birds 
breathe  much  faster  than  we  do  and  have  a  very  rapid 
circulation  of  blood.  This  causes  a  high  body  tempera- 
ture. The  body  temperature  of  birds  is  often  eight  or 
ten  degrees  Fahrenheit  higher  than  that  of  man. 

Mammals.  --The  class  of  animals  known  as  mammals 
includes  man,  a  large  number  of  quadrupeds  such  as  the 
dog,  cat,  sheep,  pig,  horse,  and  cow,  and  a  few  animals 
like  the  whale  and  seal.  They  are  called  mammals  be- 
cause they  nurse  their  young  with  milk  secreted  by  glands 
known  as  mammary  glands.  Other  characteristics  of 
mammals  are  their  covering  of  hair,  well-developed  lungs, 
and  a  highly  developed  nervous  system. 

Most  of  the  mammals  live  on  land.  Some,  like  the 
seal  and  sea  lion,  inhabit  islands  and  waters  near  the  land ; 
a  few,  like  the  whale,  live  in  the  ocean.  These  animals 
are  variously  adapted  to  their  particular  kind  of  life. 
Some  live  in  trees  ;  others  burrow  in  the  ground.  Some 


ANIMAL  LIFE  361 

eat  only  flesh  ;  while  others  eat  nothing  but  plants.  Some 
bring  forth  their  young  well  developed  to  a  form  similar 
to  their  own,  while  others,  like  the  kangaroo,  carry  their 
immature  young  in  a  pouch  on  the  under  side  of  the  body 
until  they  are  able  to  care  for  themselves. 

Animals  used  as  Food.  --The  lowest  forms  of  animals 
are  not  used  by  man  as  food.  However,  these  animals 
are  eaten  by  higher  for.ms  of  animals,  and  they  in  turn 
become  the  food  of  man. 

Mammals,  birds,  fish,  mollusks,  crustaceans,  amphibia, 
and  reptiles  are  extensively  used  as  food.  Among  the 
mammals  and  birds  so  used  are  many  game  and  domestic 
animals.  The  number  of  edible  varieties  of  fish  is  large. 
The  different  varieties  of  turtles  are  used  as  food  by  nearly 
all  peoples  of  the  earth. 

Oysters  and  clams  are  sold  in  large  quantities  as  food. 
The  oyster  industry  is  one  of  the  most  profitable  of  our 
fisheries  and  furnishes  employment  to  a  large  number  of 
men.  The  most  productive  oyster  grounds  are  Long 
Island  Sound,  Chesapeake  Bay,  and  Narragansett 
Bay. 

Among  the  crustaceans  lobsters  and  crabs  are  valuable 
foods.  More  than  twenty  million  lobsters  are  taken 
annually  along  the  north  Atlantic  coast. 

In  addition  to  the  animals  which  are  used  directly  as 
food  there  are  many  animal  products  which  are  so  used, 
such  as  butter,  cheese,  and  honey. 

Animal  Products  used  for  Clothing.  —  Wool  is  a  very 
valuable  animal  product  (Figure  322).  After  the  wool  is 
cut  from  the  sheep  it  is  cleaned,  carded,  and  woven  into 
cloth. 

The  silkworm  or  caterpillar  furnishes  all  of  the  real 
silk  that  we  have.  The  worm  lives  upon  leaves,  prin- 


362 


GENERAL   SCIENCE 


FIG.  322.  —  Shearing  Sheep,  New  South  Wales,  Australia. 

cipally  those  of  the  mulberry,  and  makes  a  cocoon  from 

which  the  silk  is  obtained  (Figure  323). 

Furs  from  wild  and  domesticated  animals  are  exten- 
sively used  for  cloth- 
ing. The  seal  is  the 
most  valuable  fur- 
bearing  animal. 

Leather  manufac- 
ture is  one  of  the 
industries  of  any  civi- 
lized country.  In  the 
United  States  there 
are  a  large  number 
of  manufacturing 

plants  distributed  through  the  states  in  the  eastern  part 

of  our  country. 


FIG.  323.  —  Evolution  of  the  Silkworm. 


ANIMAL  LIFE 


363 


Animals  which  Aid  Man.  —  A  great  many  animals 
aid  man  by  destroying  harmful  insects.  The  toad  lives 
on  insects  and  because  of  this  fact  is  a  valuable  animal. 
It  is  estimated  that  a  full-grown  toad  will  eat  from  one 
hundred  to  two  hundred  insects  daily. 

Birds  are  also  economically  important  for  the  same 
reason.  The  diet  of  our  native  birds  includes  many 
insects  which  are 
harmful  to  useful 
plants. 

Certain  insects 
do  a  valuable 
work  in  distribut- 
ing the  pollen  of 
plants. 

Animal  Pests. 
-The cotton  boll 
weevil  has  at- 
tracted much  at- 
tention in  recent 
years  because  it 
has  proven  so 
very  destructive 
to  a  most  im- 
portant crop.  It 
is  estimated  that 
if  the  pest  should 
become  generally 
distributed  over 
the  cotton  belt, 
the  possible  annual  loss  may  easily  reach  $250,000,000. 

The  adult  beetles  pass  the  winter  in  various  places  in 
or  near  the  cotton  fields.  In  the  spring  they  attack  the 


U.  S.  Dept.  of  Agriculture. 
FIG.  324.  —  Work  of  the  Cotton  Boll  Weevil. 


364 


GENERAL  SCIENCE 


young  plants,  feeding  upon  the  buds  and  laying  eggs  in 
some  of  the  holes  which  they  make  in  them.  These 
eggs  soon  hatch  into  grubs  that  immediately  begin  to 
feed  upon  the  interior  of  the  buds,  thus  destroying  the 
blossoms  and  with  them  the  prospects  of  a  crop  (Figure 
324) .  In  a  few  weeks  these  grubs  (larvae)  change  to  pupae 
and  then  to  adult  beetles  which  gnaw  their  way  out  and 
are  ready  to  lay  eggs  for  a  new  brood  of  larvae. 


FIG.  325.  —  Stages  in  the  Development  of  the  Colorado  Potato  Beetle. 

At  the  left  are  the  eggs ;  in  the  center  the  beetle,  life-size  and  enlarged  ; 
and  at  the  right  the  larva. 

The  most  effective  way  to  combat  the  cotton  boll 
weevil  seems  to  be  to  gather  all  the  cotton  plants  late  in 
the  autumn  and  burn  them,  after  which  the  ground  should 
be  plowed  to  expose  the  hibernating  places  of  the  bug. 

Other  destructive  beetles  are  the  Colorado  potato  bugs, 
the  striped  cucumber  beetle,  and  curculios. 

The  Colorado  potato  beetle  has  made  its  way  from  the 
Rocky  Mountain  region  to  nearly  every  part  of  the  world. 


ANIMAL  LIFE  365 

The  accompanying  cut  shows  the  various  stages  in  its 
development  (Figure  325).  They  are  readily  killed  by 
the  use  of  stomachic  poisons. 

The  worminess  of  plums  and  cherries  is  largely  due  to 
the  curculio  (Figure  326).  The  plum  curculio  appears  in 
fruit  trees  in  early  spring  and  feeds  on  the  leaves  and  fruit. 
The  females  also  cut  crescent-shaped  holes  in  the  fruit  and 
deposit  their  eggs.  In  from  three  to  seven  days  these 
eggs  hatch  into  little  grubs  that  feed  on  the  fruit.  As 
a  usual  thing  the  infested  fruit  falls  to  the  ground  in  a 

short  time.     The    . 

grub  then  leaves 
the  fruit  and  bur- 
rows into  the 
ground,  changing 
later  to  the  beetle  

/  T     \      o*  Ohio  Agricultural  Experiment  Station. 

(curcuho).  Spray-  F[o  m _ The  p]um  Curcu[.o 

ing  with  arsenical 

poison  just  as  the  blossoms  are  falling  is  an  adequate 

remedy  for  curculio. 

Scale  Insects.  —  An  examination  of  the  leafy  branches 
of  the  apple  tree  will  often  show  what  appears  like  minia- 
ture shells  upon  the  bark.  These  are  the  Oyster  Shell 
Scale.  If  the  shell  is  lifted  there  will  usually  be  found 
a  number  of  small  eggs  under  it.  These  eggs  hatch 
early  in  the  summer.  The  small  insects  that  develop 
wander  on  the  bark  of  the  tree,  finally  fixing  themselves 
in  one  place  to  feed  on  the  sap  which  they  suck  from  the 
bark. 

The  San  Jose  Scale. --The  presence  of  this  noto- 
riously destructive  scale  at  first  is  difficult  to  detect  with- 
out the  aid  of  a  good  magnifying  glass.  Figure  327  shows 
the  appearance  of  the  individual  scales.  As  the  scales 


366 


GENERAL  SCIENCE 


FIG.  327.  —  The  San  Jose  Scale. 


increase  in  number  they  form  a  thick  layer  of  scurf, 

which  is  readily  removed  with  some  sharp  instrument. 

They  suck  the  sap  and  thus 
weaken  the  tree  by  withdraw- 
ing the  food  that  the  tree  re- 
quires. In  the  spring  the 
mature  female  scales  give  birth 
to  about  four  hundred  young. 
These  soon  fasten  themselves  to 
the  bark  of  the  tree  and  begin 
to  suck  the  sap  and  grow  the 
scale  which  covers  them.  The 
female  scales  are  without  wings, 
but  the  male  scales  develop 
wings  and  are  able  to  fly  about. 

The    best    treatment    for   them    is    lime-sulphur   spray. 

Figure  328  shows  the  effect  of  this  scale  on  the  pear. 
The    Codling   Moth.  —  Millions   of   dollars   worth   of 

fruit  are  annually  destroyed  by  this  pest.     It  lays  its 

egg  on  the  young   apple.      When   the 

larva  hatches,  it  eats  its  way  into  the 

apple.      Young    apples    thus    affected 

usually  fall  before  they  are  very  large. 

The  way  to.  kill  the  codling  moth  is  to 

have  some  poison  on  the  apple  ready 

for  the  first  meal  of  the  larva.     This 

can  be  accomplished  by  spraying  with 

arsenate  of  lead  or  some  other  poison 

just  as  the  petals  are  falling  from  the 

blossom. 

The  Chinch  Bug. — The  central  states 

of  the  middle  West  are  often  infested  with  the  chinch  bug 

(Figure  329).     These  insects  attack  the  grain  plants  such 


Ohio  Agricultural  Experi- 
ment Station. 

FIG.  328.  —  The  San 
Jose  Scale  on  a  Pear. 


ANIMAL  LIFE 


367 


as  corn,  wheat,  and  oats.  They  pass  the  winter  in  any  field 
shelter  such  as  thick  grass.  In  the  spring  they  lay  their 
eggs  on  the  young  grain  plants.  The  young  bugs  suck 
the  sap  of  the  plant,  and  if  they  are  very  numerous,  the 
plant  will  be  killed.  The  best  method  of  attack  on  the 
chinch  bug  is  to  burn 
over  places  which  are 
possible  winter  quarters 
for  them. 

The  Hessian  Fly.  - 
These  flies  are  mosquito- 
like  insects  which  are 
quite  destructive  to  grow- 
ing wheat.  They  live  in 
the  larval  state  upon  the 
growing  plant.  They  lay 
their  eggs  on  the  leaves 
of  the  young  plant  in  the 
fall  of  the  year.  The 
small  larvae  which  hatch 
work  their  way  into  the 
joints  and  by  gradually 
absorbing  the  sap  they 
greatly  weaken  or  en- 
tirely destroy  the  plant. 
The  larvae  change  in  the 
late  autumn  to  the  pupal  stage  and  resemble  a  flax  seed 
in  appearance.  In  this  stage  they  pass  the  winter, 
changing  in  the  spring  to  full-grown  Hessian  flies.  These 
lay  the  eggs  for  another  generation  of  larvae  which  attack 
the  wheat  in  the  spring. 

It  is  quite  difficult  to  combat  the  Hessian  fly.     The 
mosf  successful  method  has  been  the  trap  crop.     Narrow 


urn 


£7.  S.  Dept.  of  Agriculture. 
FIG.  329.  —  The  Chinch  Bug. 


368  GENERAL  SCIENCE 

strips  of  wheat  are  planted  early  to  attract  the  fly.  After 
the  eggs  are  laid  these  strips  are  plowed  under  and  the 
wheat  planted  later  escapes. 

There  are  numerous  other  insects,  bugs,  and  moth 
larvae  which  do  considerable  damage  to  plant  life.  The 
usual  remedy  is  the  destruction  of  the  infested  parts 
and  proper  spraying. 

Poisons  for  Crop  Pests.  —  It  is  estimated  that  insects 
annually  destroy  one  tenth  of  the  crops  of  the  United 
States.  In  order  to  have  strong  healthy  plants  and  sound 
fruits,  these  ever-present  insect  pests  must  be  exter- 
minated. To  accomplish  this  result  various  poisons  have 
come  into  quite  general  use.  These  poisons  may  be 
divided  into  two  general  classes  according  to  the  type 
of  insect  that  is  to  be  destroyed.  Some  pests,  like  the 
potato  bug,  feed  directly  on  the  leaf  of  the  plant  and  may 
be  killed  by  placing  poison  on  the  leaf.  Poisons  which  are 
eaten  by  the  insect  are  called  stomachic  poisons.  Then 
there  are  other  pests  which  get  their  nourishment  by  suck- 
ing the  juices  of  the  plant  or  the  plant  leaf.  To  kill  such 
animals  it  is  necessary  to  use  a  poison  which  acts  on  the 
body  by  enveloping  it  and  drying  up  its  tissues  by  cutting 
off  its  air  supply  or  by  poisoning  it  through  absorption. 

Stomachic  Poisons.  —  Paris  green  is  a  poison  which 
is  in  quite  common  use  for  those  insects  which  swallow 
their  food.  It  is  prepared  by  combining  hot  solutions 
of  arsenious  acid  and  copper  acetate.  Paris  green  sepa- 
rates from  this  mixture  as  a  fine,  bright  green  powder, 
which  is  almost  insoluble  in  water.  However,  it  will 
readily  dissolve  in  ammonia  water,  giving  a  dark  blue 
solution.  If  the  Paris  green  is  adulterated  with  gypsum, 
a  white  powder  will  be  suspended  in  the  ammonia  water ; 
this  will  gradually  settle  to  the  bottom. 


ANIMAL  LIFE  369 

For  use  in  spraying  mix  eight  ounces  of  Paris  green  with 
a  little  water  and  mix  it  into  a  paste,  then  add  it  to  fifty 
gallons  of  water.  If  two  pounds  of  lime  are  added  to  this 
mixture,  it  will  serve  to  neutralize  any  free  arsenious  acid. 

Lead  arsenate  has  been  used  for  a  number  of  years  as 
an  insecticide.  It  is  the  most  insoluble  of  the  insecticides 
now  in  use.  It  adheres  well  to  the  leaves  and  is  not  in 
the  least  liable  to  scorch  them  as  is  Paris  green  and  London 
purple  when  not  used  with  lime. 

For  spraying  purposes  two  pounds  of  the  commercial 
paste  in  fifty  gallons  of  water  will  give  good  results. 

Contact  Poisons.  —  Lime-sulphur  is  a  common  contact 
poison.  It  is  prepared  by  heating  together  eight  pounds 
of  sulphur,  four  pounds  of  good  quicklime,  and  five  gal- 
lons of  water.  The  lime  should  first  be  slaked,  after 
which  the  sulphur  mixed  with  water  is  added.  The 
whole  mixture  is  then  boiled  for  an  hour.  More  water 
should  be  added  as  the  boiling  continues,  to  replace  that 
lost  by  evaporation.  After  the  boiling  is  completed  the 
clear  liquid  should  be  poured  off  and  placed  in  closed 
kegs  or  barrels,  since  it  oxidizes  on  coming  into  contact 
with  the  air. 

For  use  in  winter  to  exterminate  scale  insects  the  liquid 
should  be  diluted  until  it  tests  5.0  on  a  Baume*  hydrom- 
eter. For  use  as  a  summer  spray  it  should  be  diluted 
to  test  1.0  Baume*. 

Since  kerosene  will  not  mix  with  water,  an  emulsion  is 
made  by  dissolving  one  pound  of  soap  in  two  gallons  of 
water  and  adding  two  gallons  of  kerosene  to  the  solution. 
These  should  be  thoroughly  mixed  by  pumping  the  mix- 
ture through  a  bucket  sprayer. 

When  applied  to  the  surface  of  pools  of  stagnant  water, 
kerosene  kills  the  mosquito  pupa  by  suffocation. 


370  GENERAL  SCIENCE 

It  cannot  be  applied  directly  to  plants,  but  the  emulsion 
mentioned  above  may  be  used  against  all  sucking  insects 
and  scale  when  diluted  to  20  gallons. 

In  some  places  the  San  Jose  scale  on  orange  trees  is 
treated  by  inclosing  the  tree  in  a  tent  and  applying 
hydrocyanic  acid  gas.  This  gas  is  very  poisonous  and 
care  should  be  taken  that  none  of  it  is  breathed. 

Weevils  in  grains  may  be  killed  by  carbon  disulphide 
placed  in  a  dish  and  set  on  the  surface  of  the  grain.  It 
is  very  volatile,  the  heavy  vapor  settling  slowly  through 
the  entire  bin,  killing  the  insects  as  it  goes.  Care  should 
be  taken  that  no  flames  are  brought  near  carbon  disul- 
phide, as  its  vapor  is  very  combustible. 

QUESTIONS 

1.  How  do  one-celled  plants  and  one-celled  animals  differ? 

2.  What  is  the  lowest  form  of  animal  life  that  has  a  nervous 
system  ? 

3.  Why  does  an  earthworm  die  when  placed  in  the  sun? 

4.  How  may  we  most  easily  destroy  the  house  fly? 

5.  How  do  reptiles  differ  from  fishes?     From  amphibians? 

6.  How  do  birds  differ  from  reptiles? 

7.  Name  five  carnivorous  mammals.     Ten  herbivorous  mam- 
mals.    Three  omnivorous  mammals. 

8.  What  class  of  mammals  does  man  use  for  food  ? 

9.  What  amphibians  are  used  as  food  by  man?     What  mol- 
lusks?     What  is  the  lowest  class  of  animals  used  as  food? 

10.  Name  five  food  products  besides  flesh  that  are  furnished  by 
animals. 

11.  Is  the  cat  a  useful  or  injurious  animal? 

12.  Name  five  animals  that  are  useful  to  man  and  are  not  used 
as  food  by  him.     How  is  each  animal  useful? 

13.  Are  there  birds  that  are  classed  as  pests? 

14.  What  is  the  source  of  neat's  foot  oil?     Glue?     Gelatine? 
Tallow?     Ivory? 

15.  What  uses  are  made  of  animal  hair? 


ANIMAL  LIFE  371 

16.  What  is  the  most  serious  insect  pest  in  your  county? 

17.  Name  three   poisons  other  than  those  mentioned  in  the 
text  which  are  used  to  kill  insects. 

18.  Is  the  United  States  government  justified  in  spending  money 
for  the  extermination  of  crop  pests? 

19.  What  other  fruits  do  curculios  attack? 

20.  What  is  a  beetle? 


CHAPTER  XXII 

MAN'S   PLACE   IN   NATURE 

THE  student  who  has  worked  over  the  intricate 
problems  of  mensuration  .which  seem  to  have  little  con- 
nection with  his  daily  life  will  appreciate  them  all  the 
more  when  he  realizes  how  the  carpenters  and  builders 
of  centuries  ago  labored  over  these  same  problems  in 
studying  out  the  relations  of  distances  and  spaces  in  their 
work.  Also  when  the  student  knows  something  of  prim- 
itive man's  crude  methods  of  conversing  by  gestures 
and  cries  he  will  readily  appreciate  the  advantages  of 
articulate  speech  and  will  attack  the  subtleties  of  modern 
grammar  with  greater  zest.  And  so  it  is  with  the  various 
departments  of  science  with  which  man  is  concerned. 
The  study  of  man  himself  is  a  most  interesting  depart- 
ment of  these  sciences ;  but  we  are  always  studying  man, 
since  the  development  of  all  science  has  been  man's  work. 

Man's  Place  among  the  Animals.  —  Man  differs  from 
the  lower  animals  in  many  ways ;  but  the  principal  dif- 
ferences are  due  to  civilization.  The  identity  of  man 
as  an  animal  is  so  completely  hidden  in  this  maze  of 
civilization  that  his  true  position  in  the  animal  kingdom 
from  a  physiological  standpoint  is  obscured.  The  anat- 
omy of  man  differs  very  little  from  that  of  the  higher 
mammals ;  but  man's  powers  differ  to  an  almost  im- 
measurable extent.  Man's  reasoning  power  so  far  sur- 
passes that  of  the  highest  apes  that  great  naturalists 
have  been  at  loss  to  account  for  the  similarity  in  the 

372 


MAN'S  PLACE  IN  NATURE  373 

appearance  of  their  brains.  There  are  many  accounts 
of  incidents  which  seem  to  indicate  that  reasoning  power 
is  possessed  by  animals ;  however,  we  are  quite  safe  in 
saying  that  man  is  the  only  animal  that  has  reasoning 
power,  the  power  of  forming  abstract  conclusions,  and 
the  power  of  articulate  speech.  The  delicate  coordination 
in  man's  brain  is  also  reflected  in  the  various  refinements 
in  muscular  action  of  which  he  is  capable. 

Language.  —  We  can  learn  a  great  deal  about  the  dif- 
ferent races  of  mankind  by  a  careful  study  of  their  lan- 
guages. Primitive  peoples  used  various  means  for  com- 
municating with  one  another,  such  as  making  gestures, 


FIG.  330.  —  Picture  Writing. 

uttering  cries,  speaking  words,  drawing  pictures,  and 
writing  with  characters  or  letters  (Figure  330).  The 
language  was  little  enriched  from  outside  influences  ex- 
cept in  times  of  tribal  wars,  when  the  captives  would 
contribute  in  some  degree  to  the  civilization  of  their 
captors. 

Crude  methods  of  communication  among  friendly 
tribes  served  to  distribute  bits  of  knowledge  of  general 
usefulness  but  imperfectly.  Centuries  sometimes  added 
but  little  to  the  total  sum  of  human  attainments.  The 
slowly  moving  story  of  discovery  and  invention  is  neces- 
sarily intricately  interwoven  with  the  story  of  the  de- 
velopment of  language.  Modern  methods  of  rapid  com- 
munication and  travel  will  serve  to  bring  the  peoples 


374 


GENERAL  SCIENCE 


of  the  world  to  a  better  understanding  of  each  other  and 

to  minimize  the  differences  due  to  racial  tendencies  and 

environment. 

Man's  Tools  and  Weapons. --The  arts  which  man 

has  used  to  defend  and  maintain  himself  depend  so  much 

on  the  use  of  tools  and 
weapons  that  some  attention 
may  well  be  paid  to  them. 
Man  is  distinctly  a  tool- 
making  animal. 

The  club  was  probably  the 

FIG.  331. -Ancient  Grinding  Stones.    firgt    t()()1    uged    fey    m^    and 

it  was  used  principally  as  a  weapon  of  defense.  For 
centuries  he  delighted  in  clubs  ranging  from  the  formidable 
looking  knotty  ones  to  the  intricately  carved  clubs  which  we 


FIG.  332.  —  Stone  Hatchet,  Stone  Hammer,  Stone  Maul. 

see  in  the  museums  to-day.  The  hammer  was  a  club  modi- 
fied for  use  as  an  implement  of  manufacture.  It  was  a 
great  step  in  advance  when  a  handle  was  attached  to  a 
rounded  stone  to  make  a  hammer  (Figure  332).  Later 


MAN'S  PLACE  IN  NATURE 


375 


the  stone  was  ground  to  an  edge  for  a  cutting  instrument 
(Figures  333,  334). 

It  is  not  possible  to  know  just  when  a  knowledge  of 
the  mechanical  principles  was  attained.  It  is  quite 
probable  that  such  knowledge 
developed  slowly  for  centuries. 

The  use  of  metal  gave  cer- 
tain tribes  a  distinct  advantage 
over  their  adversaries.  The 

f      ,,  11  FIG.  333.  — A  Rude  Axe,  Showing 

USe      Of      the      wheel      Was      an-       a  Handle  Attached  to  a  Stone. 

other     important      discovery. 

And  so  we  might  enumerate  hundreds  of  inven- 
tions which  we  use  to-day  with  little 
thought  of  the  ages  that  were  consumed  in 
their  development. 

This  age  in  which  we  are  living  is  dis- 
tinctly the  age  of  wonderful  inventions  and 
achievements   in   all  branches   of  science. 
We  no  sooner  see  the  completion  of  a  won- 
derful mechanical  conception  than  another 
more  marvelous  attracts  our  attention. 
FIG  334 —An       The  Home. --The  animals  inferior  to 
Indian  Knife  with   man  build  their  homes  by  instinct.     They 
have  little  ability  to  modify  them  to  vary- 
ing conditions  of  climate  and  environment.     Man,  how- 
ever, has  never  been  hampered  by  any  such  restrictions, 


FIG.  335.  —  Pottery  from  Ancient  Burial  Mounds. 


376 


MAN'S  PLACE  IN  NATURE 


377 


but  has  adapted  his  dwellings  to  suit  his  environment. 
(Figure  336).  He  has  lived  in  almost  every  conceivable 
type  of  house,  from  caves  and  huts  of  skin  to  the  magnifi- 
cent structures  which  he  is  fond  of  building  to-day ;  but 
in  every  case  the  influence  of  man's  thought  is  evident  in 
these  structures  as  they  have  been  varied  to  fit  the  condi- 
tions under  which  he  lives  and  has  lived. 

In  the  conveniences  of  the  home  just  as  great  changes 
are  noticeable.  Man  has  always  had  fire  and  water,  but 
their  uses  have  been 
greatly  increased  in 
the  last  century. 

There  are  many 
mythological  tales 
concerning  the  gift 
of  fire,  but  so  far 
as  we  are  able  to 
ascertain  no  savage 
tribe  has  been  dis- 
covered that  was 
without  this  great 
blessing  (Figure 
337).  Among  the  relics  of  remotest  antiquity  pieces  of 
charcoal  and  burnt  bones  are  found.  In  his  knowledge 
of  fire  man  differs  from  all  other  creatures,  since  he  alone 
has  known  how  to  manage  and  produce  it. 

In  our  homes  the  luxuries  of  a  few  years  ago  are  neces- 
sities of  to-day.  The  modern  house  is  equipped  with 
water,  gas,  electricity,  baths,  stoves,  heating  systems, 
and  other  contrivances  which  add  greatly  to  our  enjoy- 
ment of  life ;  and  the  coming  years  will  no  doubt  add 
many  more  useful  inventions  to  our  already  enormous 
list. 


FlO.  337.  —  Indian  Method  of  Broiling. 


378  GENERAL  SCIENCE 

QUESTIONS 

1.  Can  you  give  illustrations  where  animals  seem  to  think? 

2.  Can  animals  be  taught  to  use  tools? 

3.  Name  the  races  of  man. 

4.  How  did  the  Indian  language  compare  with  ours  at  the  time 
America  was  discovered? 

5.  What  can  you  tell  of  Indian  writing? 

6.  How  were  messages  sent  from  one  tribe  to  another? 

7.  What  proofs  can  you  collect  that  birds  build  their  nests  by 
instinct  ? 


CHAPTER  XXIII 
FOODS  AND   NUTRITION 

Need  of  Food.  —  One  of  the  most  elementary  sensa- 
tions of  the  human  body  is  that  of  hunger.  It  is  simply 
a  provision  of  nature  to  tell  us  that  the  body  needs  food. 
As  we  grow  older  we  learn  that  the  food  must  be  chosen 
with  some  care  to  enable  the  body  to  grow  and  maintain 
itself  in  a  state  of  health.  All  living  matter  requires 
food,  and  food  may  be  defined  as  anything  which  a  plant 
or  animal  takes  into  its  body  as  nourishment.  Anything 
that  we  eat  or  drink  which  nourishes  our  bodies  is  food 
for  us. 

Bodily  Energy.  —  We  have  learned  that  a  machine 
which  does  work  or  produces  energy  must  have  energy 
expended  upon  it.  Our  civilization  at  all  times  demands 
supplies  of  food  energy  and  supplies  of  mechanical  energy. 
Energy  of  one  kind  may  be  changed  into  energy  of  another 
kind,  but  it  is  never  created  or  destroyed.  This  is  known 
as  the  Law  of  the  Conservation  of  Energy.  The  body  is 
often  compared  to  a  steam  engine.  When  fuel  is  oxidized 
(burned)  in  the  fire  box  of  a  steam  engine,  the  stored 
energy  in  the  fuel  is  released  as  heat  energy.  This  heat 
acts  upon  the  water  in  the  boiler  and  changes  it  to  steam, 
which  has  the  power  of  expansion.  This  power  may 
then  be  used  in  doing  mechanical  work  or  in  producing 
heat  again.  The  potential  energy  of  the  coal  is  changed 
to  kinetic  energy. 

As  in  the  steam  engine,  the  source  of  energy  in  our 

379 


380  GENERAL  SCIENCE 

bodies  is  in  the  oxidation  of  the  fuel  or  food  we  eat.  All 
the  various  manifestations  of  energy,  such  as  heat  and 
action  in  the  body,  have  the  same  source.  Since  some 
parts  of  the  body  are  always  in  action  and  since  the  body 
must  be  kept  at  constant  temperature,  there  must  always 
be  a  supply  of  food  present  in  the  body  to  supply  this 
energy. 

Measurement  of  Food  Values.  —  By  careful  experiments 
it  has  been  found  that  the  work  equal  to  lifting  427  grams 
a  distance  of  one  meter  will  produce  a  calorie  of  heat  or 
enough  heat  to  raise  the  temperature  of  one  gram  of 
water  one  degree  Centigrade.  Since  this  relation  between 
heat  energy  and  work  exists,  it  is  usual  to  give  the  values 
of  different  foods  in  terms  of  the  calories  they  are  capable 
of  producing.  Fuel  values  of  foods  are  usually  given 
in  large  calories,  or  a  calorie  equal  to  1000  of  the  small 
calories  mentioned  above  and  written  Calories.  Food 
is  actually  fuel  for  the  human  organism,  and  the  con- 
sideration of  food  on  this  rational  and  intelligible  plan 
has  furnished  a  logical  basis  for  a  constructive  study  of 
practical  dietetics  and  the  nutrition  of  the  individual. 
There  are  some  essential  food  factors  whose  value 
cannot  be  accurately  shown  in  terms  of  calories,  but 
they  are  like  the  lubricants  for  a  great  machine ;  they 
are  essential,  but  they  do  not  furnish  the  energy  to  run 
the  machine. 

Source  of  Food.  —  Agriculture  is  the  great  source  of 
food  supply.  The  rapidly  developing  transportation 
facilities  have  made  it  possible  to  utilize  profitably  an 
increasing  amount  of  the  earth's  surface  for  agriculture. 
A  hundred  years  ago  it  would  have  been  a  waste  of  energy 
to  raise  an  enormous  crop  of  wheat  in  the  inland  portions 
of  the  middle  West,  since  there  was  no  adequate  way  to 


FOODS  AND  NUTRITION  381 

market  the  crop  (Figure  338).  Now  our  transportation 
facilities  are  so  highly  organized  that  it  is  possible  to  dine 
on  various  perishable  foods  in  places  far  removed  from 
the  food  sources  (Figure  339). 

The  study  of  our  food  supply  involves  a  study  not 
only  of  food  production,  but  a  study  of  food  preservation, 


FIG.  338.  — Wheat  Harvesting. 
A  modern  oil  tractor  operating  five  binders. 

of  food  conservation,  of  transportation,  and  of  industrial 
conditions. 

Food  Preservation  as  Related  to  Food  Supply.  — 
Modern  methods  of  preserving  foods  make  it  easy  to 
maintain  a  dietary  in  times  and  places  of  relative  scarcity 
which  otherwise  would  be  impossible.  Some  of  the 
methods  of  preserving  foods  have  been  in  use  for  a  long 
time.  These  include  drying,  canning,  salting,  pickling, 
and  smoking  (Figure  340).  The  use  of  low  tempera- 
tures and  certain  chemicals  other  than  salt  for  preserving 
foods  is  of  comparatively  recent  development.  Cold 
storage  methods  have  the  great  advantage  of  preserving 


382 


GENERAL  SCIENCE 


fresh  foods  in  their  natural  state  for  an  almost  indefinite 
length  of  time  (Figure  341).  According  to  Mr.  Sher- 
man,1 "  Three  American  dairy  farms  exhibited  raw  milk 
at  the  Paris  Exposition  1900,  one  of  them  sending  weekly 
shipments  throughout  the  summer,  each  of  which  was 


Copyright,  1915,  by  Keystone  Vfew  Company. 
FIG.  339.  —  Harvesting  Pineapples  in  Florida. 

kept  on  exhibition  in  the  raw  state  without  spoilage  until 
the  next  shipment  arrived.  It  was  difficult  to  convince 
the  jury  of  European  experts  of  the  fact  that  cleanliness 
and  cold  were  the  only  preservatives  needed  to  accomplish 
the  keeping  of  raw  milk  in  a  fresh,  sweet  condition  for 

1  Professor  H.  C.  Sherman  :  Food  Products.     1914. 


FOODS  AND  NUTRITION 


383 


two  to  four  weeks  in  midsummer."  By  the  use  of  these 
methods  it  is  possible  to  supply  the  inhabitants  of  a  large 
city  like  New  York  with  fresh  milk  at  a  reasonable  price. 


IFV 


U.  S.  Dept.  of  Agriculture. 
FIG.  340.  —  Packing  Blanched  and  Cold-dipped  Product  into  Jars. 

Note  the  empty  jars  to  be  packed  inverted  in  a  pan  of  hot  water.     They 
are  thus  kept  clean  and  hot. 

Drying,  which  has  been  used  for  many  years  as  a  method 
of  preserving  certain  foods,  such  as  meats  and  fruits,  has 
some  advantages 
over  cold  (Fig- 
ures 342,  343). 
After  the  food  is 
thoroughly  dried 
it  may  be  trans- 
ported  easily  over 
long  distances. 
Early  explorers 
usually  carried 
large  quantities  of 

dried    meats.      As  FIG.  341.  —  Cooling  Room  for  Carcasses. 


384 


GENERAL  SCIENCE 


a  usual  thing,  however,  some  of  the  desirable  flavors  are 
lost  in  the  drying  process,  and  the  food  is  less  palatable 
than  fresh  food.  Modern  methods  of  drying  in  vacuum 
pans  at  lower  temperatures  have  been  quite  successful  in 
overcoming  this  objection,  and  we  shall  probably  see  an 
extension  of  the  use  of  desiccation  as  a  preservative. 
Milk  furnishes  a  good  example  of  this.  We  have  had 
partially  dried  milk  as  condensed  milk  for  some  time ; 


U.  S.  Dept.  of  Agriculture. 

FIG.  342.  —  Drying  Fruits  and  Vegetables  on  Homemade  Racks  by  Forcing 
Air  at  Room  Temperature  across  Them  by  Means  of  an  Electric  Fan. 

but  dried  milk  is  now  a  reality,  and  it  is  quite  likely  to 
supersede  other  prepared  milks  if  its  nutritive  values  are 
not  diminished  in  the  process  of  drying. 

Before  the  distribution  of  fresh  meat  was  so  well  organ- 
ized, large  quantities  of  pork  were  preserved  by  smok- 
ing and  salting.  The  hams  and  shoulders  were  smoked 
during  the  winter  months  and  thus  kept  for  use  dur- 
ing the  following  summer.  The  sides  of  the  hog  were 
placed  in  dense  brine  and  kept  in  a  cool  place.  Meat 


FOODS  AND  NUTRITION  385 

could  be  kept  in  this  way  as  long  as  desired.  These 
methods  are  still  used  in  rural  communities  with  good 
results. 

All  foods  are  subject  to  the  attack  of  destructive  bac- 
teria. The  changes  produced  in  food  by  these  bacteria 
usually  render  them  less  palatable  and  often  destroy 
their  value  as  foods.  The  various  methods  of  preserving 
foods  may  be  classed  under  the  general  heads  of  physical 


FIG.  343.  —  Drying  Codfish,  Provincetown,  Mass. 

and  chemical  methods.  To  the  first  class  belong  such 
methods  as  canning,  refrigerating  or  cooling,  and  drying 
or  evaporating.  These  methods  are  applicable  to  all 
kinds  of  foods  and  are  highly  efficient,  since  they  make 
very  slight  changes  in  the  flavor,  appearance,  and  com- 
position of  the  foods.  The  chemical  methods  of  preserv- 
ing foods  involve  a  change  of  chemical  conditions  in  the 
foods  of  such  a  character  that  decomposition  takes  place 
very  slowly.  Chemicals  used  as  preservatives  include 


386 


GENERAL  SCIENCE 


alcohol,    vinegar,    sugar,    salt,    borates,    bfcnzoates,    sali- 
cylates,  and  formaldehyde. 

Transportation  as  Related  to  Food  Supply.  —  The 
wonderful  growth  of  the  cities  in  the  last  few  decades  has 
increased  the  problems  of  food  distribution.  Managers 
of  transportation  facilities  have  been  alert,  and  keen 
competition  has  effected  many  interesting  developments 

in  the  exchange  of  com- 
modities. We  are  no 
longer  confined  to  local 
products  in  our  dietary, 
but  may  satisfy  our  taste 
with  the  foods  of  every  cli- 
mate and  region.  Fresh 
fruits  may  be  had  at  all 
times  and  in  most  places 
of  the  world,  and  their 
wide  use  is  fully  justified 
by  the  better  average 
health  of  the  users. 
Better  methods  of  pre- 
serving foods  have  made 
better  organized  trans- 
portation possible.  Con- 
versely, better  transpor- 
tation facilities  have  made 
the  preservation  of  certain  foods  profitable  to  both  the 
producer  and  the  consumer  (Figure  345). 

The  Manufacturer's  Place  in  Food  Supply.  —  A  few 
minutes'  time  spent  in  studying  the  food  advertisements 
in  the  current  magazines  and  newspapers  will  convince 
the  most  skeptical  that  the  manufacturer  has  a  very  im- 
portant part  in  the  distribution  of  certain  foods.  There 


Copy < right  by  Underwood  &  Underwood,  N.  Y. 


FIG.  344.  —  Taking  Salmon  from  Trap, 
Puget  Sound,  Washington. 


FOODS  AND  NUTRITION  387 

are  attractive  advertisements  of  "  breakfast  foods, " 
prepared  meats,  and  various  other  foods.  Of  course 
these  foods  cost  more  than  food  in  the  bulk;  but  their 
increased  use  from  year  to  year  indicates  that  people 
are  willing  to  pay  more  in  the  interest  of  food  hygiene 
and  their  own  convenience.  These  manufactured  foods 
are  perhaps  slowly  changing  our  eating  habits.  Break- 
fast is  becoming  a  meal  of  fruits  and  cereals  instead  of 
the  heavy  meal  of  fifty  years  ago.  Bread  making  in 


FIG.  345.  —  Development  of  the  Locomotive. 

some  localities  is  already  a  factory  problem,  and  with 
better  methods  of  manufacture  and  distribution  the  use 
of  baker's  bread  is  certain  to  increase. 

Nature's  Food  Factories.  —  Man's  food  must  contain 
whatever  is  needed  to  build  and  repair  the  body,  to  give 
it  fuel  for  heat  and  to  regulate  certain  processes  of  the 
body.  Plants  derive  their  nourishment  largely  from  the 
mineral  kingdom,  and  animals  derive  their  nourishment 
from  plants  and  animals  that  feed  upon  plants.  It  is 
true  that  animals  require  certain  inorganic  materials  such 
as  water  and  salt,  but  the  sources  of  real  foods  are  plants 


388  GENERAL  SCIENCE 

and  other  animals.  Plants  make  the  foods  which  they 
need  and  also  all  the  food  for  animals.  They  are  the  only 
real  food  factories. 

Kinds  of  Foods.  —  The  number  of  substances  used  as 
food  is  large,  but  these  substances  may  be  conveniently 
grouped  according  to  their  chemical  composition  and 
sources,  as  protein,  carbohydrates,  fats,  vitamines,  ash 
constituents,  and  water. 

Proteins.  —  The  proteins  are  frequently  spoken  of  as 
the  nitrogenous  foods.  They  always  contain  carbon, 
hydrogen,  oxygen,  and  nitrogen.  Proteins  are  always 
rich  in  one  or  more  such  organic  substances  as  albumen, 


FIG.  346.  —  Some  Building  Foods  that  Make  Bones  and  Muscles. 

casein,  fibrin,  gelatin,  gluten,  legumin,  and  myosin. 
The  principal  protein  food  materials  are  milk,  eggs,  flesh 
foods,  legumes,  and  cereals  (Figures  346,  347).  They 
are  the  foods  which  serve  to  build  up  the  body  and  keep 
it  in  repair. 

The  presence  of  protein  in  a  food  may  be  detected  by 
the  following  simple  experiments. 

Nitric  Acid  Test.  —  Boil  the  food  to  be  tested  in  nitric 
acid.  When  cool  add  enough  ammonia  to  neutralize  the 
acid.  If  the  yellow  nitric  acid  solution  turns  to  a  deep 
orange  when  the  ammonia  is  added,  protein  is  present. 

Biuret  Test.  -  -  To  a  ten  per  cent  solution  of  caustic 
soda  add  a  dilute  solution  of  copper  sulphate,  drop  by 


FOODS  AND  NUTRITION 


389 


drop,  until  a  faint  blue  color  appears,  but  no  precipitate. 
Now  add  the  solution  to  be  tested.  A  violet  color  indicates 
protein. 


Beans 


Eggs 


Milk 


Bread 


Cheese 


Sceak 


Rolled  Oats 


Potatoes 


FIG.  347.  —  Foods  Containing  Equal  Amounts  of  Proteins. 

Carbohydrates. --This  class  of  foods  is  made  up  of 
the  starches,  sugars,  and  glucoses,  and  enters  largely 
into  the  composition  of  foods  of  vegetable  origin.  The 
carbohydrates  contain  carbon,  hydrogen,  and  oxygen, 


FIG.  348.  —  Sugar  and  Starch  are  Foods  that  Produce  Power  and  Heat. 

as  the  name  indicates.      They  are  essentially  energy- 
producing  foods  or  fuel  foods  (Figure  348). 

Green  plants  make  all  of  the  carbohydrates  which  we 
use  as  food,  except  milk  sugar.     In  the  presence  of  sun- 


390  GENERAL  SCIENCE 

light  and  chlorophyll,  plants  make  glucose  from  the 
carbon  dioxide  and  water  which  are  taken  in  through 
their  leaves  and  roots.  This  form  of  carbohydrate  the 
plant  uses  as  food.  But  the  plant  makes  much  more 
food  than  it  needs,  and  this  is  changed  into  more  compact 
forms  of  sugar  and  starch  and  stored  in  its  roots  and  seeds. 

Sugar  and  starch  are  very  similar  substances.  In  fact 
nature  is  constantly  at  work  making  sugar  from  starch. 
The  reason  that  ripe  fruit  is  sweeter  than  green  fruit  is 
because  in  ripening  much  of  the  starch  is  changed  to 
sugar.  Similar  changes  occur  in  the  process  of  digestion. 
When  starchy  foods  are  eaten,  the  starch  is  changed  V» 
a  usable  form  of  sugar  by  the  action  of  the  digestive 
fluids. 

The  normal  functioning  of  the  body  requires  so  much 
power  that  much  more  fuel  food  is  required  than  tissue- 
building  food ;  that  is,  more  carbohydrates  and  fats  are 
needed  than  proteins.  Protein  is  both  a  tissue  builder 
and  a  fuel  food,  while  carbohydrates  when  taken  into  the 
body  unmixed  with  other  foods  are  usable  only  as  fuel 
foods  ;  however,  they  may  combine  with  nitrogen-bearing 
foods  and  aid  in  the  repair  of  tissues. 

Starch.  —  Starch  is  found  in  all  green  plants,  and  in 
tubers,  seeds,  and  tapioca  (Figure  349).  Its  presence  may 
be  detected  by  the  action  of  iodine.  A  solution  of  iodine, 
in  potassium  iodide  and  water,  colors  raw  or  cooked  starch 
blue.  The  starch  to  be  tested  should  be  cool  and  either 
neutral  or  acid  to  litmus. 

Test  a  freshly  cut  piece  of  potato  for  the  presence  of 
starch  by  putting  a  drop  of  iodine  solution  on  it.  Other 
vegetables  and  grains  may  be  tested  in  the  same  way. 
Celluloses  and  glycogen  are  related  to  starch.  Cellulose 
is  found  in  the  cell  walls  of  plants  and  is  almost  insoluble ; 


392 


GENERAL  SCIENCE 


Corn 


i.e.,  indigestible.  It  is  needed,  however,  to  give  bulk  to 
foods.  Glycogen  is  the  form  in  which  carbohydrates 
are  normally  found  after  absorption  in  the  liver  and 
muscles. 

Glucoses.  —  Common  representatives  of  this  group 
of  carbohydrates  are  known  as  dextrose  or  grape  sugar, 
levulose  or  fruit  sugar,  and  galactose.  Invert  sugar  is 

a  mixture  of  equal  parts 
of  dextrose  and  levulose. 
There  is  no  essential  dif- 
ference in  these  com- 
pounds except  in  their 
effect  on  polarized  light. 
Dextrose  in  solution  has 
a  right-hand  rotary  effect 
on  polarized  light ;  levu- 
lose, a  left-hand  effect ; 
and  galactose,  a  right- 
hand  effect. 

Dextrose  is  found  in 
ripe  fruits  and  vegetables, 
in  corn  sirup,  in  the  digestive  tract  as  the  result  of  the 
action  of  the  digestive  juices  on  sugars  and  starches,  and 
in  cooked  fruits,  due  to  the  action  of  the  fruit  acids  on  the 
sugar  used  for  sweetening.  It  is  less  sweet  than  sugar 
and  gives  a  reddish  color  when  tested  with  Fehling's 
solution. 

Levulose  is  found  as  a  companion  of  dextrose.  It  is 
much  sweeter  than  dextrose  and  does  not  crystallize 
readily.  It  gives  the  same  test  as  dextrose  with  Feh- 
ling's solution. 

Fehling's  solution  test.  —  Prepare  Fehling's  solution 
by  dissolving  6.2  grams  of  copper  sulphate,  3.5  grams  of 


Pa  ' 
Wheat 


Bean 


FIG.  350.  —  Starch  Grains  from  Various 
Foods. 


FOODS  AND  NUTRITION 


393 


Rochelle  salts,  and  2  grams  of  potassium  hydroxide  in 
100  grams  of  water. 

Cover  some  chopped  raisins  with  water  and  after  allow- 
ing them  to  stand  for  a  few  minutes  test  the  water  for 
the  presence  of  grape  sugar  by  heating  a  little  of  it  with 
about  10  cc.  of  the  Fehling's  solution.  A  reddish  precipi- 
tate indicates  dextrose  or  grape  sugar. 

Test  honey,  corn  sirup,  and  cane  sugar  in  the  same 
way. 

Contrary  to  a  current  opinion  much  advertised  by  the 
newspapers  a  few  years  ago,  glucose  is  a  wholesome  food. 
It  is  not  so  sweet  as  cane  sugar,  with  which  it  is  frequently 
mixed  because  of 
its  cheapness.  We 
buy  sugar  chiefly 
for  its  sweetness, 
and  a  pound  of 
the  mixture  will 
be  worth  less  as  a 
sweetening  agent 
than  the  pure  cane 
sugar. 

Sugars.  -  -  The 
ordinary   sugar 

Of       Commerce      is  Cutting  a  Crop  of  Sugar  Cane. 

manufactured  from  sugar  cane  and  sugar  beets  (Figure 
351).  The  sugars  include  sucrose,  maltose,  and  lactose. 
Sucrose  is  the  sugar  obtained  from  cane,  beets,  and  maple 
sap.  Maltose  does  not  occur  in  nature,  but  is  produced 
by  a  fermentation  of  the  starch  of  barley  and  other 
cereals.  Lactose  is  the  sugar  in  milk. 

Can  the  presence  of  cane  sugar  be  determined  with 
Fehling's  solution? 


394 


GENERAL  SCIENCE 


Add  a  few  drops  of  vinegar  to  a  solution  of  cane  sugar 
and  then  test  with  Fehling's  solution. 

Add  a  drop  of  hydrochloric  acid  to  a  few  cubic  centi- 
meters of  cane  sugar  solution  and  boil.  When  cool,  add 
enough  sodium  carbonate  solution  to  neutralize,  and  test 
with  Fehling's  solution.  What  change  has  the  hydro- 
chloric acid  produced? 

Fats.  -  -  These  include  ordinary  meat  fats  and  all 
vegetable  and  animal  oils.  Fats  contain  the  same  ele- 
ments as  the  carbohydrates,  but  in  different  proportions. 
The  principal  kinds  of  fats  used  as  food  are  the  fats  of 

meats,  butter,  olive 
oil,"palmoil,  cotton- 
seed oil,  and  al- 
mond oil  (Figure 
352).  They  are  in- 
soluble in  water  but 
are  readily  soluble 
in  ether,  chloro- 
form, and  gasoline. 

Fatty  foods  are  high  in  heat  value  and  form  the  prin- 
cipal diet  of  the  inhabitants  of  cold  climates.  When 
more  fat  is  digested  than  is  required  for  the  present  uses  of 
the  body,  it  is  stored  in  various  parts  of  the  body  as  a 
reserve  which  may  be  used  when  needed. 

The  vegetable  fats  of  commerce  are  in  liquid  form, 
while  the  animal  fats  are  usually  solids.  This,  however, 
is  not  true  of  the  animal  fats  in  their  original  state,  where 
they  too  are  liquids.  Fat  in  animals  occurs  as  minute 
drops  inclosed  in  tiny  sacs.  When  fresh  milk  is  allowed 
to  stand,  the  millions  of  little  fat  drops  rise  to  the  surface 
of  the  milk,  as  cream. 

Vitamines.  —  In  addition  to  the  well-known  classes  of 


FOODS  AND  NUTRITION  395 

foods  there  are  substances  occurring  in  minute  quantities 
in  certain  food  materials,  which  are  essential  to  growth 
and  complete  nutrition.  These  substances  are  called 
mtamines.  If  they  are  lacking  in  sufficient  quantities 
normal  growth  is  impeded  and  certain  diseases  result. 

Ash  Constituents.  —  Mineral  salts  and  water  belong  in 
this  class.  The  principal  minerals  which  enter  into  the 
composition  of  the  body  are  salt,  lime,  iron,  magnesia, 
phosphorus,  and  potash.  With  the  exception  of  com- 
mon salt,  these  substances  are  usually  taken  into  the 
body  only  in  combination  with  other  plant  and  animal 
foods.  , 

Water.  — While  water  may  not  properly  be  called  a  food, 
it  is  true  that  a  large  amount  of  water  is  needed  daily,  since 
it  enters  into  the  composition  of  every  tissue  in  the  body 
and  is  constantly  being  removed  by  the  organs  of  excre- 
tion. No  solid  matter  can  be  absorbed  and  pass  into 
the  blood.  All  food  must  be  dissolved  in  order  to  pass 
through  the  walls  of  the  intestine,  and  large  quantities 
of  water  are  needed  for  the  process  of  digesting  the  food. 
"Drink  plenty  of  water  every  day  "  is  an  excellent  health 
rule. 

Beverages.  -  -  Tea  and  coffee  are  in  no  sense  foods, 
since  what  proteins  and  carbohydrates  they  contain  are 
not  capable  of  being  dissolved  and  used  by  the  body. 
Chocolate  and  cocoa  have  real  food  value.  All  of  these 
drinks  are  stimulants  of  varying  strengths  and  serve 
to  increase  mental  and  physical  alertness.  The  stimu- 
lating effects  of  chocolate  and  cocoa,  however,  are  small 
as  compared  with  the  effects  of  tea  and  coffee.  The 
stimulant  in  tea  is  called  theine ;  in  coffee,  caffein ;  in 
chocolate  and  cocoa,  theobromine.  Tea  also  contains 
another  harmful  substance  called  tannin,  which  inter- 


396  GENERAL  SCIENCE 

feres  with  the  secretion  of  the  digestive  fluids  and  hence 
with  the  digestion  of  certain  foods. 

Alcohol.  —  The  action  of  the  governments  of  several 
of  the  countries  of  Europe  during  the  great  war  gives  us 
a  good  idea  of  the  trend  of  civilization  with  respect  to 
the  use  of  alcohol.  The  question  of  the  use  of  alcohol 
has  been  a  much  discussed  one  of  late  years  among  physi- 
ologists. Alcohol  is  composed  of  the  elements  carbon, 
oxygen,  and  hydrogen  and  will  to  some  extent  satisfy  the 
requirements  of  the  body  for  heat  and  muscular  energy ; 
yet  its  use  is  attended  with  dangerous  results  wholly 
lacking  in  the  use  of  carbohydrates  and  fats.  It  obstructs 
the  normal  action  of  the  liver  and  other  organs,  and  loads 
the  circulation  with  impurities  which  are  quite  harmful 
and  dangerous  to  health. 

Effects  of  Alcohol.  —  If  we  pour  some  95  per  cent 
alcohol  on  the  white  of  an  egg,  the  albumen  will  immedi- 
ately coagulate  and  present  an  appearance  similar  to 
that  of  the  coqked  white  of  egg.  This  is  because  the 
alcohol  takes  the  water  from  the  albumen.  Strong 
alcohol  taken  into  the  body  acts  in  the  same  way  and 
draws  the  water  from  the  living  protoplasm,  thus  hard- 
ening it. 

Alcohol  taken  into  the  body  in  very  small  quantities 
apparently  does  no  harm  and  is  oxidized  at  the  cells, 
but  if  we  examine  the  records  of  the  life  insurance  com- 
panies whose  results  are  obtained  by  the  averaging  of 
thousands  of  cases,  we  find  that  the  expectation  of  life 
is  greatly  decreased  by  even  the  moderate  use  of  alcohol. 
When  we  consider  its  ultimate  effects  we  must  classify 
alcohol  as  poison,  and  not  as  a  food.  Hardening  of  the 
arteries,  cirrhosis  of  the  liver,  and  various  nerve  disorders 
are  traceable  to  the  use  of  alcohol.  In  addition  the 


FOODS  AND  NUTRITION 


397 


body  is  weakened  so  that  it  becomes  an  easy  prey  to  dis- 
ease germs. 

How  Alcohol  is  Made.  —  Alcohol  is  made  by  the  action 
of  yeasts  on  fruit  or  grain  juices.  Fermentation  results 
in  changing  the  grape  sugar  to  alcohol,  the  carbon  dioxide 
passing  into  the  air. 

Patent  Medicines.  —  Many  patent  medicines  contain 
alcohol  and  other  harmful  constituents  such  as  opium, 


Cider  Beer  Wine,  Whiskey        Brandy 

FIG.  353.  —  Relative  Amounts  of  Alcohol. 

morphine,  and  cocaine.  Bitters  and  tonics  which  are  so 
widely  advertised  frequently  contain  alcohol  in  quantities 
ranging  from  15  per  cent  to  45  per  cent.  Whiskey  is 
50  per  cent  alcohol,  wines  about  10  per  cent,  and  beer 
5  per  cent  (Figure  353).  By  comparing  the  percentage 
of  alcohol  in  patent  medicines  with  the  percentages  of 
alcohol  in  the  ordinary  alcoholic  drinks,  some  idea  of  the 
dangerous  effects  of  such  medicines  may  be  easily  obtained. 


398  GENERAL  SCIENCE 

People  who  are  sick  or  who  imagine  an  ailment  are  usually 
quite  gullible  in  the  matter  of  patent  medicines.  A  col- 
lection of  articles  published  under  the  title  of  The  Great 
American  Fraud,  by  the  American  Medical  Association, 
which  deals  with  this  subject,  may  be  read  with  profit  by 
any  one. 

Tobacco.  —  A  narcotic  has  been  defined  as  a  sub- 
stance "  which  directly  induces  sleep,  blunts  the  senses, 
and,  in  large  amounts,  produces  complete  insensibility." 
Tobacco,  opium,  and  cocaine  are  narcotics.  Tobacco 
contains  a  strong  poison  known  as  nicotine.  A  few 
drops  of  pure  nicotine  would  be  sufficient  to  cause  the 
death  of  an  adult  by  its  action  upon  the  nervous  system. 
The  effects  of  tobacco  are  more  marked  on  young  people 
than  on  adults.  The  evidence  is  quite  conclusive  that 
the  use  of  tobacco  affects  the  heart  action  and  retards 
muscular  development:  The  boys  who  are  habitual 
smokers  of  cigarettes  average  smaller  in  size  than  the 
non-smokers,  and  they  average  lower  in  their  studies. 
The  cigarette  habit  seriously  handicaps  a  boy  in  his  search 
for  honors  in  scholarship,  athletics,  or  business. 

Purchase  of  Food. --When  we  consider  that  in  the 
United  States  we  annually  spend  about  $15,000,000,000 
for  food,  the  importance  of  proper  marketing  is  impressed 
upon  us.  Every  one  should  know  something  of  the 
science  of  purchasing  food,  since  such  a  large  proportion 
of  the  total  income  is  expended  for  food  and  since  so 
much  of  health  and  happiness  depends  upon  a  proper 
dietary. 

It  is  a  great  mistake  to  suppose  that  you  always  get 
the  best  when  you  pay  the  highest  price.  Fruits  are 
best  and  cheapest  in  season.  A  little  study  of  different 
fruits  will  enable  one  to  have  a  variety  of  the  best  avail- 


FOODS  AND  NUTRITION  399 

able  fruits  at  all  times  and  at  reasonable  prices.  Inex- 
pensive cuts  of  meat  when  properly  cooked  often  have 
higher  food  values  than  more  expensive  cuts.  Adulter- 
ated foods  are  always  expensive,  but  this  does  not  mean 
that  certain  substitutes  may  not  be  used  to  good  advan- 
tage. For  example  oleomargarine  is  quite  wholesome  and 
if  purchased  at  the  proper  price  may  represent  food  values 
relatively  as  high  as  the  food  values  of  more  expensive 
butter. 

The  better  grades  of  prepared  foods  and  canned  foods 
are  usually  more  wholesome  and  freer  from  harmful 
and  expensive  adulterations  than  the  cheaper  grades. 
It  is  quite  fortunate  for  the  majority  of  people  that 
expensive  foods  are  really  no  more  nutritious  than 
cheaper  foods ;  quite  often  expensive  foods  are  rich 
foods  whose  continued  use  produces  digestive  troubles. 

The  Dietary.  —  Good  health  is  absolutely  essential 
to  our  happiness  and  general  efficiency.  The  dietary 
is  so  intimately  connected  with  the  subject  of  health 
and  length  of  life  of  the  individual  that  it  should  be 
studied  with  greatest  care.  The  average  length  of 
human  life  has  increased  in  the  last  quarter  of  a  century 
because  of  the  intelligent  study  we  are  giving  to  hygiene 
and  to  nutrition. 

Taste  alone  should  not  control  our  selection  of  food. 
We  can  educate  our  tastes  so  that  we  can  enjoy  all  whole- 
some foods.  However,  in  selecting  our  foods  there  are 
some  actual  requirements  to  be  considered.  We  must 
have  some  proteins  and  we  must  have  some  carbohy- 
drates and  fats  to  furnish  the  fuel  food.  The  ideal 
ration  is  the  one  which  gives  us  as  nearly  as  possible 
the  proper  chemical  elements  in  the  proportion  that 
they  are  contained  in  the  body  (Figure  354).  The 


400 


GENERAL  SCIENCE 


results  obtained  by  specialists  in  nutrition  indicate  that  a 
man  who  does  average  muscular  work  requires  3.7  ounces 


Bread 


FIG.  354.  —  A  Day's  Ration. 

of  protein,  an  equal  amount  of  fats,  and  13  ounces  of 
carbohydrates  to  provide  the  energy  used  up  in  one 
day  and  for  the  repair  of  the  wasted  tissues. 

In  terms  of  fuel  values  At- 
water's  1  standard,  for  a  man  at 
light  exercise  is  2816  Calories ; 
410  Calories  from  protein,  930 
Calories  from  fat,  and  1476 
Calories  from  carbohydrates. 
Professor  Chittenden  of  Yale 
University  gives  as  his  standard 
for  the  same  man,  food  to  yield 
2360  Calories,  of  which  protein 
is  to  furnish  236  Calories,  fat 
708  Calories,  and  carbohydrates 

FIG.  355.  — Elements  Contained      1416    Calories.       ProfeSSOr    Chit- 

tenden's  diet  would  contain  about 

2.2  ounces  of  protein,  2.8  ounces  of  fat,  and  13  ounces 
of  carbohydrates. 


1  W.  O.  Atwater:  Principles  of  Nutrition  and  Nutritive  Value  of 
Food. 


FOODS  AND  NUTRITION 


401 


For  the  person  who  has  a  general  idea  of  the  amount 
and  proportion  of  the  food  substances  required  for 
his  daily  use  it  will  be  quite  easy  to  select  a  good  mixed 
diet  from  the  table  given  on  page  403.  A  mixed  diet 
is  quite  necessary,  since  milk  is  the  only  food  that 
contains  protein,  fat,  and  carbohydrate  in  a  proportion 
approximating  that  of  protoplasm  (Figure  355).  Milk 
can  be  used  as  the  sole  food  of  children  for  this  reason. 
By  a  careful  selection  of  foods  it  is  possible  to  obtain  the 


FIG.  356.  —  Nutritive  Values  of  Bread,  Beef,  and  Eggs. 

Fats,  black  ;  carbohydrates,  horizontal  lines ;  proteins,  vertical  lines ;  other 

parts,  water. 

proper  proportion  of  essentials  with  a  minimum  of  waste 
products  (Figures  356,  357).  A  vegetable  diet  contains 
a  great  deal  of  waste  materials  and  for  this  reason  is  less 
healthy  than  a  mixed  diet  containing  meats.  The  vege- 
tarian is  correct  in  his  contention  that  vegetables  contain 
everything  necessary  to  life,  but  it  is  quite  easy  to  select 
foods  which  contain  these  same  essentials  and  which  re- 
quire much  less  work  of  the  digestive  organs  in  their 
assimilation.  Some  animals  live  on  purely  vegetable 


402 


GENERAL  SCIENCE 


diets,  but  their  digestive  organs  are  so  modified  that  they 
easily  take  care  of  large  quantities  of  waste  materials, 
such  as  cellulose,  which  forms  the  indigestible  walls  of 
plant  cells.  The  digestive  organs  are  intended  for  work, 


Wheat 


Turnip 


Corn 


Apple 


FIG.  357.  —  Nutritive  Values  of  Different  Foods. 

Fats,  black ;  carbohydrates,  horizontal  lines ;  proteins,  vertical  lines ;  other 

parts,  water. 

but  they  should  not  be  overworked  in  separating  from 
food  an  excess  of  poisonous  wastes. 

Principles  of  Cooking.  —  Man  is  the  only  animal 
that  cooks  his  food,  although  a  number  of  animals  will 
eat  cooked  food.  Cooking  renders  food  more  digestible 
or  more  palatable;  and  either  is  a  sufficient  reason  for 
the  extra  trouble.  With  the  exception  of  fruits  only  a 
few  articles  of  food  are  eaten  in  their  natural  state. 

Cooking  has  a  marked  effect  on  meats.  Raw  meat 
is  tough  and  not  easily  pulled  apart.  Cooking  breaks 
up  the  connective  tissue  and  causes  the  muscular  fibers 


FOODS  AND  NUTRITION 


403 


TABLE    OF   FOOD   VALUES   OP  EDIBLE   PORTIONS   OF   SOME 
COMMON  FOODS 


PER  CENT 
PROTEIN 

PER 
CENT 
FAT 

PER  CENT 
CARBO- 
HYDRATES 

PER 
CENT 
ASH 

PER. 

CENT 
WATER 

FUEL 
VALUE  PER 
POUND 

Cheese,  American  . 

29. 

36. 

.3 

3.2 

31.5 

1990 

Peanuts     .... 

26. 

38.5 

24.4 

2.0 

9.1 

2490 

Leg  of  Mutton 

20. 

12.4 

0. 

1.2 

66.4 

863 

Dried  Peas    .     . 

24.6 

1.0 

62.0 

2.9 

9.5 

1611 

Dried  Beans      .     . 

22.5 

1.8 

59.6 

3.5 

12.6 

1565 

Roast  Beef    .     .     . 

22.3 

28.6 

0. 

1.3 

48.2 

1576 

Canned  Salmon 

22. 

12.8 

0. 

1.4 

64.6 

925 

Chicken    .... 

21.5 

2.5 

0. 

1.1 

74.8 

495 

Veal     

20.7 

8.3 

0. 

1.0 

70.9 

715 

Almonds  .... 

21.0 

54.9 

17.3 

2.0 

4.8 

2940 

Brazil  Nuts        .'  V 

17.0 

66.8 

7. 

3.9 

5.3 

3040 

English  Walnuts    . 

18.4 

64.4 

13. 

1.7 

2.5 

3180 

Oatmeal    .... 

16.1 

7.2 

67.5 

1.9 

7.3 

1810 

Wheat  Flour      .     . 

13.8 

1.9 

71.9 

1.0 

11.4 

1630 

Effffs 

13.4 

10.5 

0. 

1. 

73.7 

672 

Macaroni 

13.4 

.9 

74.1 

1.3 

10.3 

1625 

Oyster  Crackers     . 

10.7. 

8.8 

71.9 

1.8 

6.8 

1855 

Bread  

9.1 

1.6 

53.3 

1.0 

35. 

1200 

Rice 

8.0 

.3 

79.0 

.5 

12.2 

1620 

Green  Peas   .     .     . 

7.0 

.5 

16.9 

1.0 

74.6 

454 

Sponge  Cake 

6.6 

10. 

63.0 

4. 

20.6 

1670 

Oysters     .... 

6.2 

1.2 

3.7 

2.0 

86.9 

228 

Gingerbread       .     . 

6.0 

10.0 

64.0 

3.0 

17.0 

1678 

Squash  Pie    .     .     .- 

4.4 

8.4 

21.7 

1.3 

64.2 

817 

Tapioca    .... 

4.1 

3.0 

27.1 

1.7 

64.1 

687 

Milk         .     . 

3.4  • 

4. 

5.0 

6. 

87.0 

314 

Apple  Pie      <     .     . 

3.1 

9.8 

42^8 

1.8 

42^5 

1233 

Green  Corn  .     .     . 

2.8 

1.2 

19.0 

.3 

29.4 

455 

Potatoes   .... 

2.2 

.1 

18.4 

1.0 

78.3 

378 

Dried  Prunes     .     . 

2.1 

0. 

73.3 

.6 

79.6 

1368 

Fresh  Asparagus    . 

1.8 

.2 

3.3 

.7 

94.0 

100 

Cabbage   .... 

1.6 

.3 

5.6 

1.0 

91.5 

143 

Bananas   .     .     '.     . 

1.3 

.6 

22.0 

.8 

75.3 

447 

Butter      .     .     .     , 

1.0 

85. 

0. 

3.0 

11.0 

3491 

Adapted  from  Bulletin  28,  U.  S.  Department  of  Agriculture. 
1  gram  of  protein  gives  4  Calories ;  1  gram  of  fat  gives  9  Calories ; 
1  gram  of  carbohydrates  gives  4  Calories. 


404  GENERAL  SCIENCE 

to  lose  much  of  their  toughness.  The  common  methods 
of  cooking  meats  are  roasting,  boiling,  broiling,  or  frying. 
Of  these  methods  frying  is  the  poorest,  since  the  particles 
of  grease  and  injurious  fatty  acids  often  penetrate  tjie 
food  and  render  it  indigestible  in  the  stomach.  Roasting 
and  broiling  are  both  good  methods  of  cooking  meats, 
since  the  albumen  of  the  outside  of  the  meat  is  coagu- 
lated before  the  heat  penetrates  to  the  inside,  thus  re- 
taining the  nutritious  and  palatable  juices.  When  meat 
is  boiled  it  should  be  plunged  into  very  hot  water  at 
first,  so  that  the  coagulation  of  the  surface  proteid  will 
prevent  the  escape  of  the  juices. 

In  addition  to  rendering  it  more  palatable  and  more 
digestible  the  cooking  of  meat  is  always  advisable  as 
a  precaution  against  dangerous  bacteria  and  parasites 
which  are  occasionally  present. 

QUESTIONS 

1.  Why  do  we  require  more  food  in  winter  than  in  summer? 

2.  What  parts  of  the  body  are  always  in  action? 

3.  Name  some  foods  that  do  not  come  from  the  farm. 

4.  What  is  meant  by  the  term  "  to  pickle  "  as  related  to  foods  ? 
"  To  preserve"? 

5.  Should  formaldehyde  be  used  to  keep  milk?     Why? 

6.  How  is  sugar  used  as  a  preservative? 

7.  Name  ten  foods  that  are  eaten  but  not  produced  in  your 
community. 

8.  Name  ten  factory  foods. 

9.  What  is  the  objection  to  glucose  in  sugar? 

10.  What  is  the  result  when  cane  sugar  is  tested  with  Fehling's 
solution  ? 

11.  What  is  the  reason  for  the  Eskimo's  peculiar  diet? 

12.  Is  alcohol  a  food? 

1.3.    Why  does  alcohol  preserve  foods? 

14.  What  action  did  the  governments  of  the  warring  countries 
take  with  reference  to  alcohol? 


FOODS  AND  NUTRITION  405 

•      15.    What  is  food?     Is  hay  food? 

16.  What  is  the  advantage  of  a  mixed  diet? 

17.  Does  occupation  have  anything  to  do  with  the  amount  of 
food  required?     Illustrate. 

18.  What  are  two  uses  of  food? 

19.  Why  do  children  become  hungry  more  often  than  adults? 

20.  What  use  is  made  of  protein  in  the  body?     Of  fat?     Of 
carbohydrate  ? 

21.  How  many  Calories  would  you  consume  in  climbing  stairs 
representing  a  vertical  distance  of  ten  feet? 

.22.  Which   is    more   healthful  —  whole    wheat  flour  or    white 
flour?     Why? 

23.  Why  is  the  use  of  ice  an  economy  in  summer? 

24.  What  causes  food  to  spoil? 

25.  Why  do  not  alcoholic  drinks  quench  thirst? 

26.  What  is  digestion? 

27.  What  effect  has  cooking  upon  the  appearance  of  food? 

28.  What  change  is  produced  on  vegetables  by  cooking  which 
makes  them  more  digestible? 


CHAPTER  XXIV 
COMMUNITY  SANITATION 

Sanitation  or  Sanitary  Science  treats  of  the  mainte- 
nance of  health  and  the  prevention  of  disease.  It  deals 
mainly  with  (1)  the  factors  which  produce  disease,  and 
(2)  the  habits  and  means  which  enable  mankind  to  resist 
disease. 

Nearly  every  one  recognizes  the  laws  of  personal  hy- 
giene, but  the  broader  application  of  these  laws  to  com- 
munity hygiene  has  not  yet  received  the  attention  it 
deserves.  The  subject  of  public  health  is  quite  modern. 
In  fact  it  is  only  within  the  last  fifty  years  that  we  have 
known  anything  about  the  power  of  germs  as  disease 
producers.  •  In  1892  a  scientific  cure  for  diphtheria  was 
discovered.  In  1901  the  facts  concerning  the  develop- 
ment and  control  of  yellow  fever  were  discovered.  Scien- 
tists have  learned  the  causes  of  high  death  rates  and  the 
way  to  avoid  them. 

The  Growth  of  Cities.  -  -  This  is  a  day  of  great  cities. 
So  rapid  has  been  the  growth  of  the  cities  in  recent  years 
that  modern  engineering  skill  has  been  taxed  to  keep  pace 
with  the  problems  that  arise.  But  the  problems  are 
not  merely  the  problems  of  sanitary  engineers.  They 
are  the  problems  of  all  the  people  of  the  community 
and  state  and  must  be  recognized  as  such  if  we  are  to 
have  the  best  results. 

We  have  had  large  cities  for  many  centuries,  and  the 
occasional  pestilences  and  scourges  which  partially  depop- 

406 


COMMUNITY  SANITATION  407 

ulated  them  in  earlier  centuries  are  fearful  evidence  of 
the  low  community  standards  of  those  days  with  respect 
to  sanitary  conditions.  Many  of  these  old  cities  have 
passed  out  of  existence  or  have  been  replaced  by  others. 
When  we  contemplate  the  enormity  of  the  various 
problems  relating  to  food,  water,  sewage,  and  health  in 
a  large  modern  city  like  New  York,  we  must  marvel 
that  they  are  so  well  solved.  Wherever  the  individual 
is  located  he  needs  fresh  air,  pure  water,  wholesome  food, 
shelter,  a  clean  body,  and  beautiful  things  to  look  at. 
In  the  large  cities  his  needs  are  emphasized  by  his  depend- 
ence on  others,  and  at  the  same  time  his  obligations 
are  increased  because 
of  his  close  association 
with  others.  The  city 
is  no  longer  an  accu- 
mulation of  human  be- 
ings, but  a  highly  or- 
ganized society  whose 
interests  are  the  inter- 

ests  Of  the  State.  FIG.  358.  —  Bacteria  and  the  Point  of  a 

Bacteria.  —  There  Cambric  Needle' 

The   figure   shows    the    comparative   sizes. 
are      millions     OI      tiny   The  minute  dots  at  the  end  of  the  needle  repre- 

livine-  nre-anisrrm  in  sent  the  size  of  the  bacteria-     The  others 


arranged  around  the  needle  are  bacteria  more 
WOrld  (Figure  358).  highly  magnified.  The  sources  of  the  latter 
rpn  i  n  i  are  (a)  typhoid  fever,  (6)  diphtheria,  (c)  boils 

Lney   are    Single-Celled   or  abscesses,   (d)  tuberculosis,    (e)  sour  milk, 

bodies  and  belong   to  (/)  grip- 

the  divisions  of  plants  and  animals.  We  have  already 
learned  that  many  one-celled  plants  are  known  as  bac- 
teria and  belong  to  the  class  of  fungi. 

Man  divides  bacteria  into  good  and  bad,  according  to 
their  effect  on  the  things  which  he  wants  to  keep.  Most 
of  the  bacteria  are  useful  and  valuable  —  such  as  those 


408 


GENERAL  SCIENCE 


FIG.  359.  —  Milk-souring 
Bacteria. 


which  are  active  in  souring  milk,  making  vinegar,  pre- 
paring plant  food,  and  causing  the  decay  of  obnoxious 
dead  matter  (Figure  359).  On  the  other  hand,  when 
bacteria  cause  the  decay  of  meats, 
fruits,  and  foods  of  all  kinds,  and  the 
rotting  of  wooden  appliances  useful 
to  man,  we  call  them  harmful  (Fig- 
ure 360). 

If  the  single-celled  plant  or  bac- 
terium is  healthy,  it  grows  quite 
rapidly  and  divides  into  two  cells, 
these  two  dividing  in  turn,  and  so 
on.  We  can  easily  see  that  if  this 
division  were  kept  up  the  number  of  bacteria  would  soon 
be  overwhelming.  There  is  not  enough  space  or  food 
for  all,  however,  and  each 
bacterium  has  to  struggle 
for  existence.  Neverthe- 
less, as  it  is,  the  number  is 
countless  (Figure  361). 

Germs.  —  Certain  bac- 
teria and  a  few  one-celled 
animals  (protozoa)  are 
able  to  live  and  grow  as 
parasites  in  the  bodies  of 
man.  These  are  called 
disease  germs.  Every 
disease  is  caused  by  a 
particular  kind  of  germ. 
.When  bacteria  or  germs 
are  easily  transferred  from  one  person  to  another,  the 
disease  is  said  to  be  infectious. 

The  fact  that  germs  cause  contagious  diseases  was  not 


FIG.  360.  —  A  Bit  of  Decaying  Meat. 

magnified,   showing   the  bacteria 
that  cause  its  decay. 


COMMUNITY  SANITATION  409 

proved  until  about  1863,  although  the  theory  had  been 
proposed  one  hundred  years  before.  Among  the  great 
names  associated  with  the  gradual  development  of  bac- 
teriology (the  science  of  germs)  are  several  of  special 
interest.  Leeuwenhoek,  a  Dutch  lens  maker,  in  1683 
made  a  lens  so  powerful  that  he  could  see  minute  living 
things  in  the  scrapings  from 
teeth.  This  led  to  the  dis- 
covery and  classification  of 
bacteria.  Tyndall,  the  noted 
English  physicist,  and  the  ,  '£ 
great  Louis  Pasteur  in  1860  « 
proved  that  air,  when  free 
from  all  particles,  does  not  FIG.  SGI.  — Multiplication  of  Bac- 
cause  fermentation  and  decay, 

but  that  these  effects  are  produced  by  bacteria.  In  1882 
Robert  Koch  invented  gelatin  and  agar  culture  media 
(nutrient  substances  for  the  growth  of  bacteria)  so  that 
germs  could  be  kept  separated  and  each  kind  studied 
by  itself. 

From  the  investigations  of  these  men  and  many  others 
we  are  now  sure  that  germs  are  the  cause  of  colds,  ton- 
sillitis, diphtheria,  tuberculosis,  pneumonia,  measles,  scarlet 
fever,  typhoid  fever,  smallpox,  blood  poisoning,  malaria, 
yellow  fever,  etc.  If  we  know  that  all  these  diseases 
are  caused  by  germs  and  can  learn  the  means  by  which 
the  germs  may  be  destroyed,  it  is  now  only  ignorance  or 
carelessness  that  will  allow  an  epidemic  to  spread. 

To  prevent  the  spread  of  an  infectious  disease  several 
things  about  the  disease  and  the  germs  which  cause  it 
must  be  known,  namely  : 

(a)  The  source  of  the  germs. 

(6)   Conditions  favorable  to  the  growth  of  the  germs. 


410  GENERAL  SCIENCE 

(c)  How  germs  are  resisted  by  the  body  itself. 

(d)  How  germs  may  be  resisted  by  other  means. 
Source  of  Germs.  —  Since  the  air  is  filled  with  germs, 

many  of  them  disease-producing,  we  cannot  avoid  receiv- 
ing some  of  them  into  our  systems.  These  are  transmitted 
in  food  and  drink  and  by  contact  with  animals  or  sick 
persons. 

Conditions  Favorable  to  Growth.  —  Bacteria  thrive 
and  multiply  rapidly  if  the  surroundings  into  which  they 
are  introduced  are  favorable  to  their  growth.  Moisture, 
a  moderate  degree  of  warmth  and  darkness,  and  food 
from  animal  or  vegetable  matter  are  the  conditions  in 
which  they  thrive  best.  The  bodies  of  men  and  animals 
furnish  all  these  conditions.  Food  and  drink  are  also 
favorable  to  germ  growth. 

Resisting  Power  of  the  Body.  -  -  The  body  easily  re- 
ceives the  harmful  germs  through  its  natural  openings, 
lined  as  they  are  with  the  warm,  moist,  mucous  membrane, 
and  through  cuts  and  scratches.  The  body,  however, 
has  very  efficient  means  of  protecting  itself.  Some  of 
the  white  corpuscles  of  the  blood,  called  phagocytes, 
absorb  disease-causing  bacteria  as  their  food,  and  success- 
ful resistance  to  infectious  diseases  is  thought  to  depend 
largely  upon  the  number  and  activity  of  these  phagocytes. 
Then,  too,  the  body  produces  certain  other  substances 
which  are  germ  destroyers. 

When  disease  germs  enter  the  body,  there  are  not  enough 
of  them  to  produce  the  disease  at  once.  Usually  a  period 
of  time  varying  with  the  kind  of  disease  germ  elapses, 
before  the  symptoms  of  the  special  disease  appear.  This 
time,  known  as  the  period  of  incubation,  is  occupied  by 
the  germ  in  multiplying  and  producing  violent  poisons 
called  toxins.  These  poisons  are  absorbed  by  the  blood 


COMMUNITY  SANITATION 


411 


and  carried  throughout  the  body,  thus  poisoning  many 
other  parts  besides  those  at  first  affected.  The  cells  of 
the  body  immediately  begin  to  secrete  a  substance  to 
counteract  this  poison,  an  antitoxin.  If  the  patient  is 
vigorous  and  of  sufficient  vitality,  enough  antitoxin  will 
be  secreted  to  overcome  the  disease. 

The  power  of  these  natural  foes  of  the  germ  depends 
on  the  healthy  condition  of  the  body.     This  fact  and 


FIG.  362.  —  An  Out-of-door  Gymnasium. 

others  lead  us  to  these  conclusions :  that  we  must  keep 
the  skin,  all  openings  of  the  body,  and  all  food  and  drink 
entering  the  body,  clean ;  that  we  must  keep  the  body 
well  fed,  rested,  and  vigorous  that  it  may  act  naturally 
against  disease  (Figure  362).  It  is  only  when  the  body 
is  weakened  in  some  of  these  respects  that  the  germ  is 
able  to  thrive  sufficiently  to  bring  about  disease. 


412 


GENERAL  SCIENCE 


Food  and  Disease.  —  Contaminated  food  plays  an 
important  part  in  the  spread  of  almost  all  kinds  of  disease. 
The  body  is  able  to  cope  with  a  few  germs ;  but,  when 
millions  are  introduced  into  the  system  in  eating  a  small 
portion  of  impure  food,  the  danger  is  increased  many 
times.  We  need  to  be  especially  careful  in  regard  to  food. 

When  foods  are  handled  by  persons  with  dirty  hands  or 
clothing,  stored  in  unprotected  places,  or  hauled  uncovered 


FIG.  363.  —  A  Clean  Cow  and  a  Clean  Milker. 

through  streets,  they  acquire  millions  of  germs,  rendering 
them  unfit  for  food.  More  and  more  we  are  coming  to 
see  the  necessity  for  pure  food  and  are  demanding  of 
grocers,  butchers,  bakers,  and  milkmen  much  greater  care 
in  the  handling  and  protection  of  foods  (Figure  363). 
Since  most  germs  cannot  stand  a  very  high  tempera- 
ture, foods  that  are  well  cooked  are  rendered  free  from 
them. 


COMMUNITY  SANITATION 


413 


There  is  much  danger  also  in  food  that  has  reached  or 
is  approaching  the  spoiling  point.  Overripe  fruit  or 
decayed  vegetables  and  fish  are  frequent  causes  of  bowel 
troubles  and  ptomaine  poisoning,  ptomaines  being  the 
poisons  or  toxins  produced  in  the  decay  of  nitrogenous 
foodstuffs.  The  evils  arising  from  tainted  food  are  preva- 
lent in  hot  weather  when  the  housewife  "  economizes  " 
by  using  "  left  overs  "  of  various  foods  in  which  the  heat 
and  moisture  have  already  aided  in  the  growth  of  bacteria. 
The  garbage  can  is  the  safest  place  for  food  about  which 
there  is  the  slightest  suspicion. 

Danger  in  Milk.  —  In  discussing  the  dangers  arising 
from  impure  foods,  milk  may  be  considered  separately 
because  of  the  great  ease  with 
which  it  is  infected.  It  is 
classed  as  one  of  the  most 
frequent  distributors  of  dis- 
ease germs.  Many  epidemics 
of  scarlet  fever,  typhoid  fever, 
and  diphtheria,  have  been  due 
to  contaminated  milk.  The 
milk  becomes  infected  either 
at  the  home  of  the  dairyman, 
or  through  bottles  which  have 
been  returned  from  homes  where  there  is  disease,  and 
have  not  been  thoroughly  sterilized.  The  only  safe  plan 
in  the  latter  case  is  for  the  dairyman  to  refuse  to  accept 
milk  receptacles  from  homes  where  there  is  a  contagious 
disease  until  after  the  quarantine  is  lifted.  Even  after 
that  time  there  is  danger  that  the  proper  care  has  not  been 
taken  to  render  the  bottles  free  from  germs. 

The  dairy  from  which  our  milk  comes  should  be  visited 
by  a  health  officer,  who  should  see  that  the  place  is 


FIG.  364.  —  Milking  Time  in  a  Clean 
Barn. 


414 


GENERAL  SCIENCE 


sanitary  and  that  the  cows  are  in  a  healthy  condition 
(Figures  364/365).  Tubercular  cows  mean  infected  milk 
and  danger  to  all  who  drink  it.  In  progressive  com- 
munities the  health  authorities  investigate  dairy  condi- 
tions and  test  the  milk  at  frequent  intervals  to  see  that 
it  is  up  to  the  proper  standard  of  purity  and  richness. 

It  is  in  the  hot  summer  months  when  disease  germs 
multiply  very  rapidly  and  milk  spoils  quickly  that  the 


U.  S.  Dept.  of  Agriculture. 
FIG.  365.  — A  Clean,  Well-lighted  Dairy  Barn. 

danger  from  tainted  food  is  greatest,  especially  for  babies, 
because  their  food  is  largely  milk.  Steps  are  now  being 
taken  throughout  the  country  to  supply  fresh  milk  and 
ice  at  either  a  very  low  cost  or  free,  to  those  who  are  too 
poor  to  furnish  these  necessities  themselves.  Under 
these  conditions  the  per  cent  of  infant  mortality  is  much 
lower. 


COMMUNITY  SANITATION 


415 


Milk  may  be  pasteurized  and  rendered  free  from  disease 
germs  by  heating  it  to  a  temperature  of  68.3°. C.  (155°  F.) 
for  half  an  hour,  or  77°  C.  (170°  F.)  for  five  minutes 
(Figure  366).  If  the  milk  is  cooled  quickly  after  this 


8.  Dept.  of  Agriculture. 


FIG.  366.  —  A  Bottle  Pasteurizer. 


process  and  placed  in  a  cool  place  it  will  keep  longer  and 
be  a  safe  food  for  the  baby. 

Preservatives.  —  Milk  and  other  foods  are  often  pre- 
served by  means  of  chemicals  which  destroy  the  germs 
and  prevent  decay.  So  general  has  this  use  of  chemicals 
as  preservatives  become,  that  stringent  laws  have  been 
enacted  prohibiting  the  practice,  or  forcing  manufacturers 
to  state  on  the  labels  the  kind  and  amount  of  chemical 
used.  Many  dealers  in  foods,  and  even  housewives,  argue 
that  such  use  of  chemicals  is  proper,  as  the  process  is 
cheaper  than  canning  and  it  destroys  germs  in  food.  The 


416  GENERAL  SCIENCE 

danger  appears,  however,  in  the  fact  that  these  preserv- 
atives prevent  food  from  digesting  properly  and,  being 
poisonous,  in  time  work  serious  injury  to  the  body.  Milk 
that  has  not  been  pasteurized  or  properly  cooled  will  sour 
in  a  day's  time  in  hot  weather.  If  it  does  not  sour  it  has 
probably  been  treated  with  formaldehyde,  which  is  the 
chemical  commonly  used  for  this  purpose. 

Borax  and  boric  acid  will  make  tainted  meats  appear 
fresh.  Such  "  doctored  "  meats  are  often  made  into 
sausage.  Benzoate  of  soda  is  used  in  many  canned  and 
bottled  foods,  such  as  relishes,  pickles,  and  catsups. 

Danger  from  Water.  —  Nothing  is  more  important  to 
the  health  of  the  individual  and  the  community  than  an 


FIG.  367.  —  Interior  of  a  Ten-foot  Intake  Water  Tunnel. 

abundant  supply  of  pure  water.  To  obtain  such  a  supply 
and  to  see  that  it  continues  pure  should  be  the  serious 
concern  of  city  and  village  health  boards.  If  water 
from  rivers  or  lakes  must  be  used,  all  possible  precaution 
should  be  taken  to  establish  efficient  filtration  plants, 


COMMUNITY  SANITATION 


417 


or  have  the  intakes  far  enough  removed  from  any  con- 
tamination to  insure  comparative  purity  of  water  (Figure 
367).  If  water  is  obtained  from  wells,  they  should  be  so 
situated  that  they  will  not  be  contaminated  by  germ-laden 
seepage  water. 

Public  Drinking  Cups,  Towels,  etc.  —  No  matter 
how  many  precautions  are  taken  to  provide  pure  water, 
the  purpose  is  largely  defeated  if  we  allow  the  diseased 
and  healthy  to  use 
the  same  cup  for 
drinking.  Nothing 
is  more  dangerous 
or  disgusting  than 
the  public  drinking 
cup  as  it  has  been 
used  in  many  pub- 
lic places.  Many 
states  now  have 
laws  forbidding  the 
use  of  such  cups. 
City  streets  and 
parks,  schools,  pub- 
lic buildings,  and 
trains  are  equipped 

largely    With     Sani-  FIG.  368.  —  A  Drinking  Fountain. 

tary  fountains  and  individual  drinking  cups  (Figure  368). 
Along  with  the  drinking  cup  we  are  classing  and  abolish- 
ing the  public  towel,  comb,  and  cake  of  soap.  Paper 
towels  and  liquid  soap  are  now  well  established  public 
toilet  commodities.  Dishes  and  glasses  used  promis- 
cuously at  soda  fountains  and  improperly  washed  are 
also  coming  under  the  ban  and  are  being  replaced  by 
paper  substitutes. 


418 


GENERAL  SCIENCE 


warn 


Street  Cleaning.  —  A  number  of  diseases  may  be  trans- 
mitted by  means  of  the  floating  particles  with  which  the 
city  air  is  charged.  Air  may  be  tested  for  disease-pro- 
ducing bacteria  by  making  a  gelatin  and  agar  culture  of 
whatever  things  are  floating  in  the  air.  There  are  many 
sources  of  dust  in  the  city.  The  chimneys  pour  out  some 

of  it ;  the  traffic  on 
the  streets  gradually 
grinds  loose  material 
into  particles  that  are 
small  enough  to  be  car- 

^  SBf--*— *  r*ec^  ky  the  wind  ;  and 

•J  ±*    the    decomposition    of 

4*—  refuse  of  all  sorts  pro- 
1  duces  dust.  The  best 
method  of  preventing 
the  spread  of  diseases 
whose  germs  float  in 
the  air,  and  eliminat- 
ing obj  ectionable  street 
odors  is  a  thorough 

system  of  street  cleaning  (Figure  369).  The  streets  should 
be  swept  at  short  intervals  and  all  refuse  carted  away. 
Once  each  week  the  street  should  be  washed  clean  by 
" flushing"  it. 

Garbage,  Ashes,  and  Rubbish.  --These  wastes  should 
be  placed  in  different  receptacles  at  the  homes  so  that 
they  may  be  collected  most  economically.  Many  modern 
cities  are  now  burning  their  garbage  and  rubbish. 
This  is  an  ideal  way  of  disposing  of  it  from  a  sanitary 
standpoint.  Ashes  may  be  used  for  making  desired 
fills  near  the  city.  New  York  is  building  Rikers  Island 
with  her  ashes  and  street  sweepings.  The  garbage  is 


FIG.  369.  — A  Street  Cleaner. 


COMMUNITY  SANITATION 


419 


carried  to  Barren  Island,  where  it  passes  through  the 
reduction  plant.  The  material  that  arrives  at  Barren 
Island  is  first  loaded  into  digesters,  where  it  is  cooked 
with  hot  steam  for  several  hours.  It  is  then  placed  in 
hydraulic  presses  which  press  out  the  grease  and  oil. 
This  grease  is  placed  in  barrels  and  sold  to  the  soap 


FIG.  370.  —  Dumping  Garbage  into  a  Scow  to  be  Taken  out  to  Sea. 

making  industries.  The  remainder  of  the  digested  gar- 
bage is  used  for  fertilizer. 

When  garbage  is  permitted  to  accumulate,  it  forms  a 
breeding  place  for  flies  and  other  disease-carrying  insects. 

Flies.  —  "  Swat  the  fly  "  is  a  popular  and  praiseworthy 
slogan.  "  Fight  the  Filth  "  is  a  better  one,  for  only 
through  the  elimination  of  filth  will  the  campaign  against 
the  fly  be  successful.  Flies  breed  in  filth,  in  body  wastes 
of  animals,  manure  piles,  vaults,  etc.  As  they  grow  they 
feed  in  filthy  places.  They  enter  sickrooms  'and  gather 


420 


GENERAL  SCIENCE 


germs  which  not  only  cling  to  their  legs  but  pass  from 
theirxbodies  in  the  discharges  known  as  fly  specks.  Flies 
,^«— ™™  are  most  effective  spreaders 
L  v  1  of  disease  and  must  be  kept 

screened  away  from  sickness 
and  away  from  health.  It 
is  estimated  that  a  fly's  life 
is  spent  within  the  radius  of 
half  a  mile  from  its  breed- 
ing place.  Consequently  the 
presence  of  flies  indicates 
that  there  must  be,  in  the 
immediate  neighborhood, 
filth  in  which  they  can 
breed  (Figure  371). 

Keep  garbage  cans  cov- 
ered and  clean ;  eliminate 
manure  piles  and  heaps  of 
kitchen  waste ;  carefully 
screen  every  house.  With 
no  place  to  breed  and  little  to  eat,  flies  will  cease  to  be 
a  problem. 

Sewage  Disposal  and  Public  Health.  —  We  have  learned 
by  very  dear  experience  that  our  drinking  water  must 
not  be. polluted  by  sewage.  The  one  water  disease  which 
we  most  fear  in  the  United  States  is  typhoid  fever,  and 
the  only  way  in  which  a  large  supply  of  water  may  become 
contaminated  with  typhoid  germs  is  through  sewage 
wastes. 

In  1903  Cleveland  had  an  epidemic  of  typhoid  fever 
as  a  result  of  contamination  of  the  water  supply  by  the 
city's  sewage.  Many  people  bought  spring  water  while 
others  took  the  precaution  of  boiling  the  city  water. 


FIG.  371.  —  The  Foot  of  a  Fly, 
Magnified. 


COMMUNITY  SANITATION 


421 


After  carefully  studying  the  problem,  Cleveland  built 
a  new  intake  tunnel  extending  five  miles  into  the  lake. 
As  soon  as  it  was  opened  the  doctors  noticed  a  change 
for  the  better  in  the  typhoid  situation,  and  in  a  short 
time  the  water  was  considered  by  all  as  comparatively  safe. 
It  is  quite  common  for  cities  to  pour  their  sewage  into 
near-by  waters.  New  York  City  pours  its  sewage  into  the 


FIG.  372.  —  A  Sewage  Disposal  Plant. 
The  Imhoff  tanks,  Columbus,  Ohio. 

harbor,  Chicago  into  the  Illinois  River  through  the 
Chicago  Drainage  canal,  Cleveland  into  Lake  Erie. 
In  many  inland  cities  the  problem  of  sewage  disposal 
has  been  solved  by  the  installation  of  sewage  disposal 
plants.  They  have  proved  so  satisfactory  that  their  use 
undoubtedly  will  be  greatly  extended.  Such  plants 
purify  the  sewage  by  oxidation  and  by  the  aid  of  friendly 


422  GENERAL  SCIENCE 

bacteria  which  grow  and  prey  upon  the  harmful  bacteria 
of  the  sewage.  Columbus,  Ohio,  recently  installed  a 
sewage  disposal  plant  having  a  capacity  of  20,000,000 
gallons  daily. 

Figure  372  shows  the  new  Imhoff  tanks  that  are  in  ser- 
vice at  Columbus,  Ohio.  In  the  background  the  sprin- 
kling filters  are  shown.  The  sewage  passes  through  these 
tanks  at  a  very  low  velocity,  which  permits  the  heavier 
solids  to  settle  and  cling  to  the  sloping  sides  of  the  tanks. 
The  clarified  sewage  passes  through  the  tank  and  is 
sprayed  over  beds  of  broken  limestone  about  five  and  one 
half  feet  deep.  In  the  photograph  these  sprinkling  filters 
are  shown  in  the  background,  the  round  building  being 
the  place  from  which  the  liquor  is  distributed  by  means 
.  of  gates  to  the  sprinkling  filters. 

Typhoid  Fever.  —  In  1900  there  were  recorded  about 
350,000  cases  of  typhoid  fever  in  the  United  States,  with 
more  than  35,000  deaths.  Typhoid  germs  leave  the  body 
in  the  wastes  from  intestines  and  kidneys,  and  in  the 
sputum  when  pneumonia  develops  with  typhoid.  They 
are  carried  by  food,  water,  dust,  and  flies ;  by  oysters 
that  have  grown  in  beds  near  outlets  to  sewers ;  and  by 
raw  vegetables  which  have  been  watered  with  sewage- 
polluted  water. 

We  can  easily  understand,  then,  how  important  a  ques- 
tion is  the  disposal  of  sewage  in  considering  the  health 
of  a  community.  Terrible  epidemics  of  typhoid  may  be 
caused  in  the  following  ways :  by  throwing  body  waste 
from  a  patient  on  the  ground. near  a  stream  into  which 
it  may  be  carried  by  melting  snow,  rain,  or  high  water; 
by  disposing  of  sewage  where  it  may  enter  a  well  by  means 
of  seepage  water  (Figure  373) ;  by  turning  the  sewage 
from  one  city  directly  into  a  lake  or  river  from  which  an- 


COMMUNITY  SANITATION 


423 


other  community  obtains  its  water.     When  the  direction 

of   the   Chicago  River  was  changed  to  carry  Chicago's 

sewage   into   the   Mississippi   River   system   and   water 

'intakes  were  built  four  miles  out  in  the  lake,  Chicago's 


Double  floor  of  wood 
k       i^Boards  laid  at  rioht  angles 

1   ••'  i---^l'//7Z3  •          *\    3K 


FIG.  373.  —  A  Properly  Located  and  Constructed  Well  to  Prevent  the  Entrance 
of  Seepage  Water. 

death  rate  was  reduced  from  5.97  in  1891-1900  to  2.21 
in  1901-1910. 

If  there  is  any  reason  to  believe  that  your  water  supply 
has  been  contaminated  by  typhoid  fever  germs,  do  not 
fail  to  boil  the  water  twenty  minutes.  It  will  take  that 
long  to  kill  the  germs.  Four  per  cent  of  all  typhoid 
patients  carry  the  germs  in  their  bodies  for  from  ten  weeks 
to  two  years,  even  though  they  appear  perfectly  well.  These 
"  typhoid  carriers  "  may  give  the  disease  to  many  others. 


424  GENERAL  SCIENCE 

Colds.  -  -  The  spreading  of  infectious  diseases  may  be 
prevented  more  easily  if  we  understand  something  of  the 
nature  of  each.  A  cold,  considered  quite  harmless  by  the 
majority  of  people,  is  one  of  our  serious  diseases,  and  is 
brought  on  by  bacteria.  It  lowers  the  resisting  power  of 
the  body  and  often  leads  to  more  serious  infections  of 
throat  and  lungs  —  such  as  tonsillitis,  bronchitis,  pneu- 
monia, diphtheria,  etc.  Bacteria  of  colds  are  found  in 
the  nose,  mouth,  throat,  and  eyes.  They  are  communi- 
cated in  tiny  drops  by  coughing,  sneezing,  and  blowing 
the  nose.  They  may  be  carried  on  handkerchiefs,  or  on 
anything  that  comes  in  contact  with  the  secretions  of 
mouth  and  nose,  such  as  towels  and  drinking  cups.  One 
of  the  most  dangerous  spreaders  of  nose  and  throat  affec- 
tions is  the  disgusting  habit  of  spitting  in  public  places. 
The  multitude  of  germs  thrown  out  in  spitting,  dry  and 
become  mingled  with  the  dust  and  are  able  to  live  in  that 
state  for  several  months,  to  the  great  danger  of  those  who 
must  breathe  the  dust. 

Diphtheria.  —  One  of  the  most  dreaded  diseases,  espe- 
cially for  children,  is  diphtheria.  If  a  child  has  a  croupy 
cough  which  persists  during  the  day,  and  on  examina- 
tion the  throat  shows  small  grayish  white  patches,  a 
physician  should  be  summoned  at  once.  The  danger 
is  too  great  for  home  doctoring.  Membranous  croup,  for- 
merly considered  an  entirely  separate  disease,  is  now  known 
to  be  diphtheria  which  has  invaded  the  larynx. 

Diphtheria  germs  are  scattered  by  coughing  and  by  dis- 
charges from  the  nose  and  throat.  Too  great  care  cannot 
be  taken  in  disinfecting  or  burning  all  garments  and  cloths 
used  about  the  diphtheria  patient.  In  the  throats  of 
patients  who  have  recovered  from  diphtheria  the  germs 
may  be  active  for  months  and  infect  food,  dishes,  towels, 


COMMUNITY  SANITATION  42o 

and  clothing.     In  this  way  the  disease  may  be  passed  on 
long  after  quarantine  has  been  lifted. 

When  the  diphtheria  germ  enters  the  body,  it  produces 
a  poison  (toxin)  which  causes  the  severe  illness.  Imme- 
diately the  body  begins  to  produce  a  substance  which  is 
called  antitoxin.  If  the  body  is  able  to  produce  sufficient 
antitoxin,  the  patient  does  not  succumb  to  the  disease. 
In  cases  where  the  antitoxin  produced  by  the  patient  is 
not  sufficient  to  counteract  the  toxin,  a  liquid  called 
diphtheria  antitoxin  is  introduced  into  the  blood.  With 
this  help  the  disease  is  made  much  less  severe  and  if  tjte 
antitoxin  be  taken  as  soon  as  one  is  exposed,  theydisease 
is  often  prevented  entirely.  Since  the  use  of/antita 
has  become  general  the  percentage  of  fieaths/rom  cfiph- 
theria  has  been  very  much  smaller. 

Pneumonia.  —  Pneumonia,  one  of  our  most  fatal  dis- 
eases, spreads  in  practically  the  same  way  as  colds  and 
throat  infections.  Its  action  is  quite  rapid.  Pneumonia 
germs  may  be  found  in  the  throats  of  almost  all  people ; 
but  as  long  as  the  body  is  strong  and  vigorous,  it  is  able 
to  resist  them.  It  is  when  the  system  is  weakened  by 
cold  or  some  minor  disease  that  the  germs  are  able  to 
do  their  work.  Keeping  our  bodies  in  the  best  possible 
condition  is  the  only  effective  means  of  preventing  this 
disease. 

Tuberculosis.  —  "  The  Great  White  Plague  "  costs  the 
United  States  many  lives  each  year,  and  millions  of  dollars 
in  caring  for  its  patients.  Tuberculosis  or  consumption 
is  caused  by  germs  which  lodge  in  and  attack  any  part  of 
the  body,  —  bony,  muscular,  or  mucous.  Those  that 
affect  the  lungs  probably  reach  them  through  the  ali- 
mentary canal  and  the  blood. 

Most  of  the  people  in  the  world  are  attacked  by  the 


426 


GENERAL  SCIENCE 


tuberculosis  germ  at  some  time  but  easily  overcome  it 
and  are  none  the  wiser.  If  the  disease  once  gains  a  foot- 
hold on  the  body,  however,  it  becomes  more  and  more 
difficult  to  throw  it  off  because  the  system  continually 
grows  weaker.  We  are  now  positive  that  consumption 
in  its  early  stages  can  be  wholly  cured  and  that  there 

is  hope  for  those 
in  more  advanced 
stages  if  they  are 
willing  to  make  the 
effort  to  get  well. 

The  remedies  are 
simple  and  within 
the  reach  of  almost 
every  one.  They 
are  :  to  live  in  the 
open  air  day  and 
night ;  to  wear 
warm  clothing ;  to 
eat  plenty  of  plain, 
nourishing  food, 
especially  fresh 
milk  and  eggs. 

FIG.  374. -A  Sleeping  Porch.  The  ^    ^  that 

people  suffering  from  tuberculosis  must  live  in  a  warm 
climate  the  year  around  and  be  protected  from  every 
breeze,  has  been  discarded  as  wholly  false.  According 
to  the  modern  theory  the  disease  can  be  cured  at  home 
in  any  climate,  though  cool  dry  air  is  best.  A  sleeping 
porch,  tent,  or  open  air  cottage  is  the  main  requirement, 
backed  by  determination  on  the  part  of  the  patient  to 
get  well  (Figure  374).  ,-• 

Tuberculosis  germs  escape  from  the  body  in  discharges 


COMMUNITY  SANITATION 


427 


from  the  nose,  throat,  and  bowels.  They  enter  other 
bodies  on  infected  fingers  put  into  the  mouth ;  on  food 
infected  by  flies  and  other  insects  ;  or  by  milk  and  butter 
from  tubercular  cattle ;  on  dishes,  garments,  and  cloths 
used  in  the  care  of  patients.  The  sputum  from  a  con- 
sumptive should  never  be  allowed  to  dry.  It  should 
be  received  in  sputum  cups  or  on  papers  and  cloths,  and 


m 


FIG.  375.  —  The  Sun  Parlor  of  a  Large  Hospital. 
Sun  is  an  excellent  destroyer  of  germs. 

these  should  be  burned.  Children  do  not  inherit  tuber- 
culosis from  their  parents ;  but  they  may  inherit  a  weak 
resisting  power  so  that  they  succumb  to  the  disease  more 
easily  than  the  children  of  healthy  parents. 

Scarlet  Fever  and  Measles.  —  These  diseases  are  char- 
acterized by  eruptions  and  are  very  infectious,  both  oc- 
curring chiefly  in  childhood.  The  after  effects  of  both 
these  diseases  are  much  more  to  be  feared  than  the  dis- 
eases themselves.  Pneumonia  and  consumption,  weak- 
ened sight  and  hearing,  and  other  infirmities  may  follow 
if  the  greatest  care  is  not  taken  when  the  patient  is  recov- 


428  GENERAL  SCIENCE 

ering.  The  danger  of  spreading  scarlet  fever  lasts  as 
long  as  the  dead  skin  is  "  peeling  off,"  a  process  which 
continues  after  the  patient  has  otherwise  recovered. 

Smallpox.  —  Smallpox  is  one  of  the  eruptive  diseases, 
the  sores  being  of  a  loathsome  nature  and  leaving  the 
disfiguring  "  pock  marks  "  if  great  care  is  not  taken.  This 
disease  was  once  a  terrible  scourge,  and  even  up  to  the 
beginning  of  the  nineteenth  century  almost  everybody 
expected  to  have  it. 

The  first  attempt  at  preventing  the  disease  came  with 
the  discovery  that  milkmaids  who  had  become  infected 
with  cowpox  (smallpox  of  the  cow)  either  did  not  get 
smallpox  or  had  very  light  cases.  This  fact  in  1796  led 
Sir  Edward  Jenner  to  experiments  which  brought  about 
the  discovery  of  vaccination.  He  took  the  matter  formed 
in  cowpox  and  introduced  this  vaccine  virus  (poison  from 
cows)  into  the  blood  of  man.  The  germs  from  cowpox  are 
so  much  weaker  than  those  that  come  from  smallpox  that 
they  cannot  produce  the  latter  disease;  but  they  cause 
the  body  to  produce  the  substance  which  kills  the  small- 
pox germ.  The  length  of  time  for  which  vaccination 
renders  one  immune  varies  with  the  person  vaccinated, 
lasting  usually  from  one  year  to  ten  or  twelve  years. 

When  vaccination  is  attended  by  ill  effects  in  other  parts 
of  the  body  or  with  very  serious  inflammation  at  the  point 
of  vaccination,  we  may  be  sure  that  the  trouble  may  be 
laid  to  carelessness.  The  opening  of  the  skin  must  be 
kept  clean  and  free  from  other  infection. 

Diseases  Carried  by  Insects.  —  A  few  diseases  are 
caused  by  one-celled  animals  or  protozoa.  The  protozoa 
do  not  cause  disease  by  being  carried  directly  from  one 
person  to  another,  but  must  live  for  a  while  in  the  body 
of  some  insect.  The  germs  are  sucked  up  in  the  blood 


COMMUNITY  SANITATION  429 

which  the  insect  draws  when  biting  a  diseased  person. 
These  germs  live  in  the  body  of  the  insect  for  some  time, 
multiplying  rapidly.  When  they  are  ready  to  be  injected 
into  new  victims,  they  pass  into  the  salivary  glands  of 
the  insect.  From  there  they  are  injected  into  the  blood 
of  the  one  bitten,  where  they  multiply  and  produce  the 
disease. 

Malaria.  —  This  disease  was  formerly  believed  to  be 
due  to  damp  night  air  or  swamp  air.     We  now  know  that 


FIG.  376.  — A  Breeding  Place  for  Mosquitoes. 

malaria  is  caused  by  the  action  of  small  parasites,  protozoa, 
which  flourish  in  the  body  of  the  mosquito.  The  fact 
that  mosquitoes  are  more  active  at  night  and  breed  ex- 
tensively in  swamps  accounts  for  the  mistaken  ideas 
concerning  malaria. 

If  mosquitoes  can  be  kept  from  biting  people  who  have 
malaria  and  then  from  biting  other  people,  the  malaria 
question  is  solved.  Since  mosquitoes  breed  in  stagnant 
water  and  damp  places,  all  puddles,  ditches,  and  swamps 
should  be  drained,  or  treated  with  kerosene  (Figure  376). 
The  kerosene  treatment  is  very  effective  where  other 
means  are  not  practical.  The  adult  mosquito  lays  its 


430 


GENERAL  SCIENCE 


eggs  in  little  groups  on  the  surface  of  stagnant  water. 
When  the  eggs  hatch,  the  larvae  (larva)  come  forth,  little 
squirming  insects  commonly  known  as  wrigglers.  The 
larvae,  or  wrigglers,  after  about  seven  days,  change  into 
another  form  called  pupae  (pupa).  The  pupa  lives  in 
the  water  three  days  or  longer  and  changes  into  the  adult 

mosquito,  which  in 
turn  lays  eggs  and 
begins  a  new  cycle 
of  life  (Figure  377). 
When  kerosene  or 
crude  oil  is  poured 
on  the  water,  it 
spreads  over  the 
surface,  forming  a 
film  which  pre- 
vents the  larvae  and 
pupae  from  getting 
air  from  the  surface 
water  and  thus 
kills  them.  The 
adult  mosquitoes 
also  cannot  lay 
their  eggs  on  the 
surface  of  the 
water  because  they 
become  entangled 
by  the  film  of  oil. 
The  above  precautions  and  the  careful  screening  of  houses 
will  reduce  malaria  to  a  minimum. 

Yellow  Fever.  —  This  disease  is  spread  in  the  same 
manner  as  malaria  with  one  marked  difference ;  namely, 
that  while  malaria  is  carried  by  one  variety  of  mosquito 


FIG.  377.  —  Life  History  of  the  Mosquito. 

The  common  mosquito  (Culex).  A,  egg  raft; 
B,  eggs ;  C,  young  "  wrigglers  "  or  larvae ;  D  and  E, 
vi3ws  of  larvae ;  F,  pupa ;  G,  male ;  H  and  /,  fe- 
males. A,  B,  C,  G,  H,  and  /,  somewhat  enlarged. 
D,  E,  and  F,  very  much  enlarged.  (After  Howard.) 


COMMUNITY  SANITATION 


431 


called  anopheles  (Figure  378),  yellow  fever  is  carried  by 
another  species  called  stegomyia  (Figure  379) .  The  name 
of  our  common  mos- 
quito, which  is  con- 
sidered comparatively 
harmless,  is  the  Culex 
(Figure  380). 
One  of  the  main 

duties    Of    the    United     FlG>  378' ~The  Malarial  Mosquito  (anopheles). 

States  in  taking  up  the  administration  of  Cuba  and  the 
work  of  the  Panama  Canal  was  the  extermination  of 
the  yellow  fever  and  malaria  mosquitoes.  This  was  ac- 
complished by  drain- 
ing and  filling,  and 
by  a  thorough  clean- 
ing up  of  filth  of 
various  sorts  (Figures 
381,  382). 

Several  other  dis- 
eases are  spread  by  protozoa  in  the  bodies  of  insects. 
The  terrible  sleeping  sickness  of  Africa  is  caused  by  the 
Tsetse  fly ;  the  bubonic 
plague  is  carried  by  a 
kind  of  flea  which  infests 
rats;  and  the  spotted 
fever  and  cattle  fever  by 
species  of  ticks. 

Quarantine. — There  is 
one  general    method    of 

preventing  the    Spread  Of          FIG.  380.  —  The  Harmless  Mosquito 

germs  which  is  used  in 

dealing  with  all  kinds  of  infectious  diseases.     This  is  the 

setting  apart  from  the  community  of  an  individual  or 


FIG.  379.  —  The  Yellow  Fever  Mosquito 
(stegomyia) . 


432 


433 


434  GENERAL  SCIENCE 

thing  known  or  believed  to  be  infected.  Individuals  may 
be  quarantined  or  isolated  in  a  single  room  and  there  all 
precaution  taken  to  prevent  the  spread  of  the  disease  to 
other  members  of  the  household.  Sometimes  the  house 
in  which  live  one  or  more  victims  of  disease  is  quaran- 
tined to  prevent  persons  from  entering,  or  what  is  more 
dangerous,  leaving  the  house.  Ships  are  often  prevented 
from  entering  port  for  days  or  even  for  weeks  because  the 
health  authorities  have  reason  to  believe  that  passengers 
or  goods  have  been  infected. 

If  we  are  truly  in  earnest  in  our  campaign  against 
disease,  we  must  respect,  and  insist  on  others  respecting, 
quarantines.  We  may  suffer  great  inconvenience  some- 
times because  of  the  restrictions  which  quarantine  im- 
poses, but  we  must  remember  that  it  is  an  essential  factor 
in  solving  the  health  problem. 

Disinfectants.  —  Any  process  by  which  germs  are 
destroyed  may  be  spoken  of  as  disinfection.  The  sub- 
stance used  is  called  the  disinfectant.  Disinfection  which 
is  accomplished  by  means  of  gases  is  called  fumigation. 

The  common  household  disinfectants  are  soap  and  hot 
water.  Sunlight  and  air  are  great  destroyers  of  germs. 
Their  effectiveness  has  been  known  to  generations  of 
housewives  who  have  hung  clothes  and  bedding  on  the 
line  to  "  air."  Intense  heat  is  a  most  efficient  method  of 
killing  germs.  Dishes  used  by  diseased  persons  may  be 
rendered  harmless  by  placing  in  boiling  water  for  a  few 
minutes.  Typhoid  germs  in  water  and  on  articles  used 
by  patients  can  be  killed  by  boiling  twenty  minutes. 
Articles  such  as  bandages  and  surgical  dressings  may 
be  rendered  sterile  (free  from  germs)  by  subjecting  to 
great  heat  for  some  time. 

Many  chemicals  are  used  as  disinfectants.     The  most 


COMMUNITY  SANITATION  435 

common  of  these  are  unslaked  lime,  chloride  of  lime, 
carbolic  acid,  mercuric  chloride,  sulphur,  and  formalde- 
hyde. Great  care  should  be  taken  in  using  these  sub- 
stances because  most  of  them  are  poisons.  Unslaked 
lime  may  be  scattered  on  the  ground  to  disinfect  damp, 
filthy  places.  Chloride  of  lime  is  a  good  disinfectant  for 
garbage  cans  and  closets.  Carbolic  acid,  a  very  strong 
poison,  is  a  general  disinfectant.  A  solution  of  it  may  be 
used  for  many  purposes :  during  house  cleaning  for  wip- 
ing up  floors  and  washing  out  closets  and  cupboards; 
as  a  disinfectant  in  cleansing  wounds  (weak  solution) ; 
to  mix  with  the  water  in  which  clothes  are  boiled  after 
being  used  in  the  care  of  the  sick.  Mercuric  chloride 
(corrosive  sublimate,  a  deadly  poison)  is  used  in  much  the 
same  way  as  carbolic  acid.  Its  odor  is  not  so  strong, 
and  it  is  not  so  hard  on  the  skin. 

Sulphur  dioxide  and  formaldehyde  are  the  chemicals 
commonly  used  for  fumigating.  Sulphur  dioxide  is  now 
generally  obtained  by  burning  sulphur 
candles,  but  is  not  of  much  value  unless 
the  air  of  the  room  where  it  is  burned  is 
full  of  moisture.  This  may  be  accom- 
plished by  boiling  water  for  some  time 
previous  in  the  room  to  be  fumigated. 
There  is  on  the  market  however  a  com- 
mercial fumigator  which  is  quite  satis- 
.  factory,  the  moisture  being  secured  by 
setting  the  fumigator  in  water.  For-  FIG.  383.— AForm- 
maldehyde  is  a  better  disinfectant  than  aldehyde  candle' 
sulphur  dioxide.  It  is  also  used  in  the  form  of  candles 
(Figure  383),  but  it  is  more  commonly  used  in  the  form 
of  a  liquid  solution.  Cloths  are  dipped  in  the  solution 
and  are  then  hung  in  the  room  which  is  to  be  disinfected. 


436    .  GENERAL  SCIENCE 

In  order  that  the  gases  may  have  time  to  complete  their 
work  and  be  most  effective,  rooms  and  houses  which  are 
being  disinfected  by  fumigation  should  always  be  tightly 
closed  during  the  process  of  fumigation  and  allowed  to 
remain  closed  for  several  hours. 

QUESTIONS 

1.  How  does  the  body  resist  disease? 

2.  What  are  the  incubation  periods  for  scarlet  fever,  measles, 
diphtheria,  hydrophobia? 

3.  Has  your  town  a  food  inspector?     Are  tests  of  milk  and  ice 
cream  made  frequently? 

4.  Does  pasteurizing  milk  affect  its  digestibility? 

5.  What  is  meant  by  Federal  meat  inspection? 

6.  What  is  the  death  rate  for  your  town?     How  does  it  compare 
with  other  cities  of  the  country? 

7.  How  does  your  community  obtain  its  water?     How  does  it 
dispose  of  sewage  ?     Garbage  ? 

8.  How  do  the  city  and  country  compare  in  healthf ulness  ? 

9.  Can  you  name  a  disease  which  at  the  present  time  is  con- 
sidered incurable? 

10.  How  are  you  fighting  flies? 

11.  Why  should  we  all  be  interested  in  community  sanitation? 


APPENDIX 
I 

VAPOR   PRESSURES   OF   WATER 

NOTE.  —  Both  the  Fahrenheit  (F.)  and  the  Centigrade  (C.)  tempera- 
tures are  given. 


TEMPERATURE 

PRESSURE  IN 

MM. 

TEMPERATURE 

PRESSURE  IN 

MM. 

F. 

C. 

F. 

C. 

14° 

-10° 

2.2 

62.6° 

17° 

14.4 

15.8 

-  9 

2.3 

64.4 

18 

15.4 

17.6 

-  8 

2.5 

66.2 

19 

16.3 

19.4 

-  7 

2.7 

68.0 

20 

17.4 

21.2 

-  6 

2.9 

69.8 

21 

18.5 

23.0 

-  5 

3.2 

71.6 

22 

19.7 

24.8 

-  4 

3.4 

73.4 

23 

20.9 

26.6 

-  3 

3.7 

75.2 

24 

22.2 

28.4 

-  2 

3.9 

77.0 

25 

23.5 

30.2 

-   1 

4.2 

78.8 

26 

25.1 

32.0 

0 

4.6 

80.6 

27   ' 

26.5 

33.8 

1 

4.9 

82.4 

28 

28.1 

35.6 

2 

5.3 

84.2 

29 

29.8 

37.4 

3 

5.7 

.   86.0 

30 

31.5 

39.2 

4 

6.1 

87.8 

31 

33.4 

41.0 

5 

6.5 

89.6 

32 

35.4 

42.8 

6 

7.0 

91.4 

33 

37.4 

44.6 

7 

7.5 

93.2 

34 

39.6 

46.4 

8 

8.0 

95.0 

35 

41.8 

48.2 

9 

8.6 

96.8 

36 

44.2 

50.0 

10 

9.2 

98.6 

37 

46.7 

51.8 

11 

9.8 

100.4 

38 

49.3 

53.6 

12 

10.5 

102.2 

39 

52.0 

55.4 

13 

11.2 

104.0 

40 

54.9 

57.2 

14 

11.9 

105.8 

41 

57.9 

59.0 

15 

12.7 

113.0 

45 

71.4 

60.8 

16 

13.5 

212.0 

100 

760.0 

437 


438  GENERAL  SCIENCE 


II 

Fungicides.  —  Most  of  the  harmful  fungi  may  be  killed 
by  the  use  of  Bordeaux  mixture.  It  is  made  with  differ- 
ent amounts  of  copper  sulphate  and  lime  according  to  its 
intended  use. 

BORDEAUX  MIXTURE 

Copper  sulphate    .     .     .     .    2,  3,  4,  5,  6,  pounds 

Lime equal  to  copper  sulphate 

Water 50  gallons 

There  should  always  be  enough  lime  to  give  an  alkaline 
reaction  on  litmus  paper ;  otherwise  the  leaves  may  be 
scorched.  It  should  be  remembered  that  Bordeaux  mix- 
ture is  especially  effective  on  fungi  and  has  very  little 
effect  on  plant  insects. 


INDEX 


Absorption  of  light,  233 
Acetic  acid,  273 
Acetylene,  244,  263 
Acids,  272,  273,  274 
Adenoids,  91 
Adhesion,  46 
Adiabatic  heating,  157 
Aeroplane,  69 
Agonic  lines,  190 
Air,  73,  85,  213 

a  mixture,  87 

importance  to  body,  88,  89 

functions  of,  152 

movements  of,  163 

as  conductor,  197,  199 

and  sound,  213 
Albumen,  388 
Alcohol,  264,  396-397 
Algse,  329 
Alkalies,  274 
Alluvial  deposit,  309 
Ammonium  hydroxide,  274 
Ammonium  nitrate,  276 
Amrebse,  350 

Amorphous  substances,  105 
Amphibians,  359 
Analysis,  277 

of  chemicals,  278 

of  soils,  288 
Anemometer,  164 
Aneroid  barometer,  77 
Animals,  350,  361 

one-celled,  350 

as  food,  361 

clothing  from,  361 
Anode,  208 
Anther,  318 
Anti-toxin,  411 
Anti-trade  winds,  164 
Ants,  356 

Aqueous  humor,  237 
Arc  lamps,  203 
Archimedes'  principle,  116 
Aristotle,  15 
Artesian  wells,  115 


Ash,  395 
Asteroids,  2 
Astigmatism,  239 
Atmosphere,  73,  152 

density  of,  73,  154 

depth  of,  73 

composition  of,  73,  87 

weight  of,  74 

pressure  of,  75,  157 

functions  of,  152 

colors  of,  153 

temperature  of,  156 

movements  of,  163 
Atoms,  27,  194 
Auditory  canal,  216 

Bacteria,  86,  273,  294,  331,  351,  407 

Baking  powders,  269 

Balance,  34 

Barometer,  75 

Bases,  272,  274 

Bees,  356 

Beetles,  364 

Bell,  electric,  206 

Beverages,  395 

Big  Dipper,  10 

Birds,  360 

Biuret  test,  388 

Black  knot,  348  / 

Blade,  326 

Blight,  pear,  344 

potato,  344 
Blizzard,  171 

Body,  resisting  power  of,  410 
Boiling  point,  100-101,  134-135 
Bordeaux     mixture,     276,     344,     348, 

appendix 
Brass,  252 
Breathing,  89-90 
Brickfielders,  171 
Bronchial  tubes,  89 
Brown  rot,  343 

Caissons,  80 
Calcium  hydroxide,  274 
439 


440 


INDEX 


Calcium  phosphate,  276 

Calorie,  137,  380 

Calyx,  318 

Cambium  layer,  326 

Camera,  223,  229,  237 

Candle  power,  223 

Canis  major,  10 

Canker,  344,  346 

Cafions,  307 

Capillaries,  89 

Capillarity,  48 

Capillary  water,  289,  297,  310 

in  soils,  289,  290,  297 
Carbohydrates,  328,  389 
Carbolic  acid,  262,  435 
Carbon,  203,  257 

compounds  of,  259 
Carbonates,  270 
Carbon  dioxide,    73,    257,    267,    268, 

321,  328,  331 
Carburetor,  243 
Carpels,  318  t 

Casein,  388 
Cassiopeia,  10 
Cathode,  208 
Caves,  300 

Celestial  Meridian,  19 
Cells,  electric,  200 

voltaic,  200 

polarized,  201 

gravity,  201 

dry,  201 

of  living  matter,  316,  317,  319,  351 
Cellulose,  323,  390 
Centigrade  scale,  98,  100,  129 
Center  of  gravity,  39 
Cepheus,  10 
Charcoal,  84,  260,  261 
Chemical  changes,   95,   222,   246,   247 

source  of  heat,  127 
Chile  saltpeter,  87,  254,  274,  293 
Chinch  bug,  366 
Chloride  of  lime,  255 
Chlorine,  255 
Chlorophyll,  326,  390 
Choroid  coat,  236 
Cilia,  352 

Ciliary  ligament,  237 
Ciliary  processes,  237 
Cinematograph,  41 
Citric  acid,  273 
Cities,  growth  of,  406 

problems  of,  407 

cleaning  streets  of,  418 


Climate,  152,  283 

Clothing,  361 

Clouds,  175 

Coal,  259,  261 

Cochlea,  217 

Cocoa,  395 

Codling  Moth,  366 

Coffee,  395 

Cohesion,  46 

Coke,  84,  261 

Colds,  91,  424 

Cold  storage,  110,  381 

Color,  233 

Combustion,  83,  247 

Comets,  2,  5 

Compounds,  27,  247,  272 

of  carbon,  259 

classes  of,  272 
Compressed  air,  80 
Compression,  126,  127 
Concave  lens,  228 
Condensers,  197 
Conduction  of  heat,  140,  141 
Conductivity,  140 

of  earth,  142 

and  sensation,  142 

of  metals,  251 
Conductors,  193,  197,  277 
Conjunctiva,  235 
Conservation,  291 

of  soil,  291 

of  rainfall,  297 

of  energy,  397 
Constellations,  8,  9 
Convection,  143-145 
Convex  lens,  228 
Copper,  252 
Copper  sulphate,  275 
Cornea,  236 
Corolla,  318 
Cotton,  340 
Cotton  boll  weevil,  363 
Crystalline  lens,  230 
Crystallization,  104 
Crystals,  104 
Cultivation,  soil,  296 
Curculio,  365 
Cyclones,  165 
Cyclonic  winds,  165 

Dairy,  model,  413 
Davy  safety  lamp,  143 
Decay,  284,  285,  413 
Declination,  190 


INDEX 


441 


Deltas,  308,  309 
Density,  35 

of  solids,  118 

Deposition,  by  streams,  308-309 
Dew,  175 
Dew  point,  174 
Dextrose,  392 
Dialysis,  51 
Dietary,  399,  402 
Diffusion,  49,  226 
Digestion,  328,  401 

in  plants,  328 
Diphtheria,  424 
Dipping  needle,  191 
Diseases,  342 

in  plants,  342 

infectious,  408    • 
Disinfectants,  434 
Distillation,  122,  253 
Dog  Star,  11 
Doldrums,  164 
Draco,  10 

Drainage,  299,  310,  311 
Dry  farming,  297,  310 
Drying  of  foods,  383 
Dynamo,  208 

Ear,  214,  216 

Earth,  a  planet,  1,  14-18,  23 

Ebullition,  134 

Echoes,  214 

Eclipse,  222 

Elasticity,  45,  46 

Electric  arc,  203 

currents,  200,  202 

lighting,  202,  244. 

heating,  202 

bell,  206 

power,  209 

motors,  211 

Electrical  charges,  193,  195,  197 
Electricity,  191 

by  friction,  191 

positive,  192 

negative,  192 

theory  of,  194 

atmospheric,  199 
Electrodes,  93 
Electrolysis,  93,  208,  276 
Electrolytes,  276 
Electromagnets,  205 
Electrons,  194,  220 
Electrophorus,  198 
Electroplating,  208 


Elements,  27,  247-248 
Energy,  37,  41,  222 

kinetic,  41 

potential,  41 

of  body,  379 

conservation  of,  379 
Engines,  steam,  44,  70-71 
Epidermis,  326 
Epiglottis,  89 
Equatorial  calms,  164 
Equilibrium,  40 

Erosion,  304,  306-307,  335,  336 
Ether,  220 

Eustachian  tube,  217 
Evaporation,  105-106,  297,  336 
Expansion,  in  solids,  130 

in  liquids,  131 

in  gases,  132 
Experiment  stations,  296 
Explosives,  45 
Eyes,  230,  235-237 

Fahrenheit  scale,  98,  100,  129 

Fats,  394 

Fehling's  solution,  392 

Fermentation,  269 

Ferns,  329 

Fertility,  284,  286,  291 

Fertilization,  319 

Fertilizers,  292-295 

Fibrin,  388 

Filament,  318 

Filtration,  122,  422 

Fire,  origin,  264 

Fire  damp,  262 

Fire  extinguisher,  268 

Fireless  cooker,  142 

Fishes,  358 

Flashing  point,  264 

Flies,  355,  419 

Flowers,  317 

parts  of,  318-319 
Focal  length,  228 
Focus,  228 
Food,  379 

as  fuel,  380 

values,  380 

sources  of,  380,  387 

preservation  of,  381,  415 

transportation  of,  386 

classes  of,  388 

purchase  of,  398 

and  disease,  412 
Foot,  30 


442 


INDEX 


Foot  pound,  44,  55 
Force,  37 

centrifugal,  43 

muscular,  43 

gravitational,  43 

of  expanding  gases,  44 

of  wind,  43,  68 

molecular,  45 
Forests,  337 

Formaldehyde,  346,  348,  435 
Friction,  63 

a  source  of  heat,  126 
Frogs,  359 
Frost,  175 
Fruits  as  food,  340 
Fuels,  259,  266,  338 
Fulcrum,  55 
Fumigation,  434 

Fungi,  329-330,  342,  345,  348,  407 
Fungicides,  348,  appendix 
Fusibility,  251 
Fusion,  133 

Galactose,  392 
Galileo,  37 
Galvani,  200 
Garbage,  418 
Gas,  242 

artificial,  243,  262 

natural,  243,  263 

acetylene,  244 
Gases,  26,  255 
Gelatin,  388 
Gelatin  cultures,  409 
Germination,  320 
Germs,  408,  410 
Glaciated  soil,  285 
Glass,  240 
Glucoses,  392 
Gluten,  388 
Glycogen,  392 
Gold,  255 
Gram,  39 

Gravitation,  17,  37 
Ground  water,  299-300,  310 
Guncotton,  274 

Hail,  178 

Health,  240,  406-436 
Hearing,  216,  218 
Heat,  126,  202,  220,  247 

a  form  of  energy,  126 

sources  of,  126,  259 

effects  of,  130 


Heat  —  Cont. 

quantity  of,  137 

capacity,  137 

of  fusion,  138 

conduction  of,  140 

from  electric  current,  202 
Heating  systems,  147-148,  202,  266 
Hercules,  10 
Hessian  fly,  367 
Horse  latitudes,  164 
Horse  power,  44,  65 
Humidity,  151,  173 
Humus,  284,  292 
Hurricanes,  166 
Hydra,  353 
Hydraulic  press,  114 
Hydrocarbons,  259,  262 
Hydrochloric  acid,  273 
Hydrogen,  94-97,  272,  274 

Ice,  100,  108-109 

Igneous  rock,  281 

Incandescent  bodies,  220 

Incandescent  lamps,  203 

Incandescent  mantles,  243,  263 

Incidence,  angle  of,  225 

Inclined  plane,  53,  61 

Incubation,  period  of,  410 

Inertia,  42 

Inland  seas,  302 

Insects,  355,  356,  365,  368,  428 

Insulators,  193 

Invertebrates,  358 

Iris,  236 

Iron,  251 

Irrigation,  297,  310-314 

Irritability,  315 

Isobars,  154 

Isogonic  lines,  190 

Isotherms,  158 

Jack  screw,  62 
Jupiter,  2,  3 

Kerosene,  242,  264 
Kilogram,  32 
Kindling  point,  264 
Kinetic  energy,  41 
Koch,  Robert,  409 

Lachrymal  fluid,  235 
Lactose,  393 
Lakes,  302,  303 
Lamps,  143,  242 


INDEX 


443 


Language,  development,  373 

Larvae,  355 

Larynx,  89 

Latent  heat,  138 

Latitude,  21 

Lavoisier,  83 

Leaves,  317,  326 

parts  of,  326 

as  food,  340 
Leeuwenhoek,  409 
Legumin,  388 
Lens,  227,  228,  239 
Levees,  309 
Levers,  53-56 
Levulose,  392 
Leyden  jar,  197 
Light,  220-234 

properties  of,  220    • 

as  energy,  222 

intensity  of,  223 

reflection  of,  224 

diffused,  226 

refraction  of,  226 

composition  of,  231 

absorption  of,  233 
Lighting,  electric,  202,  244 

in  the  house,  240 

artificial,  241-244 
Lightning,  182 
Lime,  295 

Limestone,  270,  282 
Liquids,  26 

shape  of  free,  47 

capillary  action  in,  49 

transmission  of  pressure,  112 
Liter,  32 
Litmus,  272,  274 
Little  Dipper,  10 
Living  matter,  315 
Longitude,  21 
Lumbering,  337 
Luminous  bodies,  221 
Lungs,  88-89 

Machines,  53-54,  63 
Magnetism,  186-188 
Magnets,  186 

earth  as,  190 
Malaria,  429 
Malleability,  251 
Maltose,  393 
Mammals,  360 
Man,  372-375 
Mantle,  incandescent,  243 


Mars,  2,  3 
Marsh  gas,  262 
Mass,  34 
Matches,  265 
Matter,  26,  246 

forms  of,  26 

properties  of,  28 

changes  in,  246 
Measles,  427 
Measurement,  29 

length,  33 

volume,  34 

mass,  34 

temperature,  128 

light,  223 

Mechanical  advantage,  63 
Medullary  rays,  324 
Melting  point,  133 

in  metals,  252,  255 
Mercury,  planet,  2,  3 
Mercury,  252 
Meridians,  20 
Metals,  250-251 
Metamorphic  rock,  281 
Meter,  31 
Metric  system,  31 
Microscope,  229 
Mildews,  344 
Milk,  384,  388 

danger  from,  413 

pasteurized,  415 
Mixtures,  247 

Moisture,  need  of,  in  the  air,  151 
Molds,  331,  347 
Molecules,  28,  126 

relation  to  heat,  137 

relation  to  light,  220 
Monsoons,  172 
Moon,  11,  12 
Mosquitoes,  429-431 
Mosses,  329 
Motors,  electric,  211 
Mushrooms,  330 
Myosin,  388 

Neptune,  2,  3 
Newton,  Sir  Isaac,  37 
Nimbus  clouds,  177 
Nitric  acid,  273,  274 
Nitrogen,  85 

use  in  explosives,  86 

importance  to  plants,  86,  291,  293, 

332 
Nitroglycerine,    274 


444 


INDEX 


Noise,  214 

North  Star,  8 
Nucleus,  316 
Nutrition,  379 

Opaque  bodies,  221 
Organs,  317,  352 
Orion,  10 

Osmosis,  50,  322,  354 
Oxidation,  83,  247 
Oxides,  83,  247,  272         . 
Oxygen,  81,  247,  272,  321 

Parallels,  20 

Paramecium,  352 

Parasites,  331,  342 

Pascal's  law,  112 

Pasteur,  Louis,  409 

Patent  medicines,  397 

Peach  leaf  curl,  348 

Peat,  259 

Penumbra,  222 

Perseus,  10 

Petroleum,  263 

Phagocytes,  410 

Pharynx,  89 

Photographic  plate,  223,  229,  254,  276 

Photometer,  224 

Physical  changes,  95,  246,  247 

Pitch,  215 

Planetary  winds,  164 

Planetoids,  2,  5 

Planets,  1,  2 

Plants,  316 

reproduction  in,  319 

distribution,  332 

food  plants,  339,  387 

textile  plants,  340 

diseases  of,  342 
Pleura,  88 
Pneumonia,  425 
Poisons,  368-369 
Poles,  93,  186,  208 
Pole  Star,  9 
Pollen,  318 
Pollination,  319 
Potash,  270,  274,  294 
Potassium  hydroxide,  274 
Potato  scab,  345 
Potential  energy,  41 
Power,  44,  65 

of  water,  66 

of  wind,  68 

electric,  209 


Precipitation,  173,  178 
Preservation,  of  forests,  337 

of  foods,  381 
Preservatives,  415 
Pressure,  74,  154 

in  liquids,  110 

transmission  of,  112 
Prevailing  westerlies,  164 
Priestley,  Joseph,  81 
Prime  meridian,  20 
Prism,  231 
Properties,  28 

general,  28 

special,  29 
Protein,  87,  388 
Protoplasm,  315-316,  351 
Protozoa,  408 
Ptomaines,  413 
Pulley,  54,  58 
Pumps,  77-78 
Pupil,  230 

Quarantine,  431 

Radiation,  145 

Rain,  178 

Rainfall,  178,  299 

Rain  gauge,  180 

Rainbow,  232 

Reflected  light,  224 

Refraction  of  light,  226,  231 

Reproduction  in  plants,  318,  319 

Reptiles,  360 

Resistance,  40,  41 

Respiration,  84,  88 

Retina,  230 

Revolution,  23 

Rivers,  300,  306 

Rocks,  281,  283 

relation  to  soils,  287 
Rcemer,  220 
Roots,  317,  321,  340 
Rotation,  18 
Rust,  iron,  83 

wheat,  342 

Salt,  254 

as  preservative,  384 
Salts,  272,  275 
Sanitation,  406 
San  Jose  scale,  365 
Saprophytes,  331 
Sapwood,  324 
Satellites,  2,  3 
Saturation,  102,  173 


INDEX 


445 


Saturn,  2,  5 

Scale,  insects,  365 

Scarlet  fever,  427 

Scheele,  Carl  W.,  81 

Science,  246 

Sclerotic  coat,  236 

Scorpius,  10 

Screw,  53,  62 

Seasons,  23 

Sedimentary  rock,  281 

Seeds,  319,  340 

Separator,  43 

Sewage,  disposal  of,  420 

Shadows,  222 

Sight,  235 

Silt,  308 

Silver,  254 

Silver  nitrate,  276 

Siphon,  79 

Sirius,  11 

Smallpox,  428 

Smut,  348 

Snow,  178 

Soaps,  270,  275 

Sodium,  253 

Sodium  hydroxide,  274 

Soil,  280,  288,  341- 

formation  of,  284 

composition  of,  286 

particles,  288 

conservation  of,  291 
Soil  water,  310 
Solar  system,  2 
Solids,  26 
Solutions,  101,  102 
Sori,  332 
Sound,  212,  214,  216 

reflection  of,  214 

voice  and  hearing,  216 
Specific  gravity,  35 
Specific  heat,  138 
Spectacles,  228 
Spectrum,  solar,  231,  233 
Sperm  cell,  319 
Spirogyra,  329 
Spores,  330,  343,  345 
Spraying,  344-348,  365-369,  appendix 
Starch,  328 

in  foods,  390 
Stars,  2,  6,  8,  9 
Steam,  41,  44,  70,  100 
Steel,  252 
Stems,  323,  324 

as  food,  340 


Stoves,  266 
Stratus  clouds,  177 
Street  cleaning,  418 
Submarines,  117 
Substances,  26 
Sucrose,  393 
Sugar,  328,  390,  393 
Sulphates,  276 
Sulphur,  256 
Sulphuric  acid,  273,  274 
Sun,  13,  14,  127,  221 
Suspension,  102 
Suspensory  ligament,  238 

Tartaric  acid,  273 

Taurus,  10 

Tea,  395 

Telegraph,  206 

Telephone,  207 

Telescope,  229 

Temperature,  126 
measurement  of,  128 
of  atmosphere,  156 
relation  to  sound,  213 

Thermograph,  158 

Thermometer,  128 

Thermos  bottle,  143 

Thermostat,  149 

Thunderstorms,  180 

Time,  21 

Time  belts,  22 

Tinctures,  102 

Tissues,  316 

Toadstools,  330 

Tobacco,  398 

Tone,  214 

Tools,  development,  374 

Tornadoes,  166 

Torricelli,  76    7    . 

Toxins,  410 

Trachea,  89 

Trade  winds,  164 

Trees,  335 

value  of,  335-336 
uses  of,  337,  339 

Tuberculosis,  425 

Turbines,  water,  68 
steam,  71 

Tympanic  membrane,  217 

Typhoid  fever,  422 

Umbra,  222 
Universe,  1 
Uranus,  2,  3 


446 


INDEX 


Vacuum,  212 
Vaporization,  134 
Veins,  317,  326 
Ventilation,  147,  149 
Venus,  2,  3 
Vertebrates,  358 
Vibrations,  of  sound,  212 

of  light,  220 
Vinegar,  273 
Vitamines,  394 
Vitreous  humor,  237 
Voice,  216 
Volatile  liquids,  106 
Volta,  200 
Voltaic  cells,  200 
Volume,  34 

Water,  93,  290,  299,  395,  416 

electrolysis  of,  93 

freezing  of,  98 

uses  of,  108,  120 

pressure,  110 

city  supply,  112,  120,  123 

gravitational,  290 

ground  water,  299 

and  food,  395 

danger  from,  416 
Water  power,  66,  68 


Waterspout,  170 
Watt,  James,  44 
Waves,  sound,  212-213 

light,  220,  232 
Weather,  152 

weather  bureau,  183 
Weathering,  283,  285 

erosion,  304 
Weapons,  374 
Wedge,  54,  62 
Weeds,  341 
Weight,  38 
Wheat  rust,  342 
Wheel  and  axle,  54,  59 
Windlass,  60 
Winds,  163,  164,  171 
Wood,  259,  260 

uses  of,  337 
Work,  37,  53,  54 
Worms,  353 


Yard,  30 
Yeast,  269 

plants,  331,  349 
Yellow  fever,  430 


Zenith,  20 


18 


35754 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


